BY  THE  SAME  AUTHORS 

Elementary  Electro -Technical  Series 

COMPRISING 

Alternating  Electric  Currents. 
Electric  Heating. 

Electromagnetism. 

Electricity  in  Electro-Therapeutics. 

Electric  Arc  Lighting. 
Electric  Incandescent  Lighting. 
Electric  Motors. 

Electric  Street  Railways. 
Electric  Telephony. 

Electric  Telegraphy. 

Cloth,       Price  per  Volume,        $1.00. 


Electro-Dynamic  Machinery. 
Cloth,  $2.50. 


THE  W.  J.  JOHNSTON  COMPANY 

253  BROADWAY,  NEW  YORK 


ELEMENTARY  ELEOTKO-TECHNICAL  SERIES 

.ELECTRIC 
INCANDESCENT    LIGHTING 


BY 

EDWIN  J.  HOUSTON,  PH.  D. 


\\ 

AND 


A.  E.  KENNELLY,  Sc.  D. 


NEW  YORK 

THE  W.  J.  JOHNSTON  COMPANY 

253  BROADWAY 

1896 


COPYRIGHT,  1896,  BY 
THE  W.  J.  JOHNSTON  COMPANY. 


PREFACE. 

THIS  little  volume  has  been  prepared  by 
the  authors  with  the  view  of  presenting 
both  the  art  and  science  of  practical  electric 
incandescent  lighting  to  the  general  public, 
in  such  a  manner  as  shall  render  it  capable 
of  being  understood  without  any  previous 
technical  training. 

The  necessity  of  some  general  knowl- 
edge of  the  principles  underlying  the  prac- 
tical applications  of  incandescent  lighting, 
will  be  appreciated  from  the  fact  that  at 
the  present  time  incandescent  lamps  are 
manufactured  in  the  United  States  at  a 
rate  of  about  eight  millions  per  annum. 
This  of  course  represents  a  large  amount 

iii 


iv  PREFACE. 

of  invested  capital,  only  a  small  portion  of 
which  is  engaged  in  the  actual  manufacture 
of  the  lamps,  by  far  the  greater  part  being 
invested  in  the  central  stations  where  the 
electric  current  is  generated,  and  in  the 
streets  and  buildings  where  the  conductors 
and  fixtures  are  provided.  Since  the  whole 
of  this  important  industry  has  practically 
come  into  existence  since  1881,  compara- 
tively little  opportunity  has  been  afforded 
to  the  public  of  acquiring  a  fair  under- 
standing of  the  subject. 

It  is  in  the  hope  of  meeting  the  above 
want  that  the  authors  have  written  this 
book. 

PHILADELPHIA, 

June  1,  1896. 


CONTENTS. 


I.   ARTIFICIAL  ILLUMINATION,  1 

II.   EARLY  HISTORY    OP    INCANDESCENT 

LIGHTING,         .         .         .         .         .18 

III.  ELEMENTARY  ELECTRICAL  PRINCIPLES,       43 

IV.  PHYSICS  OF  THE  INCANDESCENT  ELEC- 

TRIC LAMP,       ...  .65 

V.    MANUFACTURE      OF     INCANDESCENT 
LAMPS.      PREPARATION   AND   CAR- 
BONIZATION OF  THE  FILAMENT,         .       83 
VI.    MOUNTING  AND  TREATMENT  OF  FILA- 
MENTS,     ......       99 

VII.    SEALING-IN  AND  EXHAUSTION,     .         .118 
VIII.    LAMP  FITTINGS,  .         .         .         .135 

IX.    THE  INCANDESCENT  LAMP,  .         .163 

X.    LIGHT  AND  ILLUMINATION,  .         .198 

XI.   SYSTEMS  OF  LAMP  DISTRIBUTION,        .     210 

XII.   HOUSE  FIXTURES  AND  WIRING,  .     237 


Vi  CONTENTS. 

CHAPTER  PAGE 

XIII.  STREET  MAINS,         ....     284 

XIV.  CENTRAL  STATIONS,          .        .        .304 
XV.   ISOLATED  PLANTS,    .        .        .        .324 

XVI.   METERS, 334 

XVII.   STORAGE  BATTERIES,        .         .         .345 
XVIII.   SERIES  INCANDESCENT  LIGHTING,     .     374 
XIX.   ALTERNATING  -  CURRENT      CIRCUIT 

INCANDESCENT  LIGHTING,       .         .386 
XX.   MISCELLANEOUS    APPLICATIONS    OF 

INCANDESCENT  LAMPS,            .         .     402 
INDEX, 419 


ELECTRIC  INCANDESCENT 
LIGHTING. 

CHAPTER  I. 

AETIFICIAL   ILLUMINATION. 

t 

DOUBTLESS,  the  earliest  artificial  illumi- 
nant  employed  by  primitive  man  was  the 
blazing  fagot,  seized  from  the  fire.  The 
step  from  this  to  the  oil  lamp  marked  an 
era  in  civilization,  since  man's  work  was 
then  not  necessarily  limited  in  time  by  the 
rising  and  setting  of  the  sun.  It  is  diffi- 
cult, at  this  time,  to  estimate  properly  the 
great  boon  to  civilization  this  invention 
afforded.  Although  at  first  sight  it  does 
not  seem  to  be  a  very  great  step  from  the 


2        ELECTRIC   INCANDESCENT  LIGHTING. 

flickering  light  of  the  torch  to  that  of  the 
oil  lamp,  yet,  when  we  consider  the  re- 
quirements of  an  artificial  illuminant,  the 
superiority  of  the  latter  is  evident  in  what 
may,  perhaps,  be  regarded  as  the  most  essen- 
tial requirement  of  such  an  illuminant ; 
namely,  its  duration;  i.  e.,  the  length  of 
time  during  which  it  can  supply  a 
proper  illumination  without  renewal.  In- 
stead of  the  fitful  flickering  of  the  torch 
we  have  the  comparatively  steady  glow 
of  the  oil  lamp ;  instead  of  the  evanescent 
light  of  the  torch,  we  have  in  the  oil 
lamp  a  means  for  furnishing  light  for 
many  hours. 

Fortunately,  for  the  sake  of  progress, 
man's  ingenuity  was  not  arrested  by  this 
great  achievement.  There  followed  in  its 
wake,  various  improvements  in  forms  of 
oil  lamps,  but  this  illumiuant  sufficed  to 


ARTIFICIAL   ILLUMINATION.  3 

light  the  world  for  many  centuries,  as  the 
tombs,  parchments  and  bas  reliefs  of  the 
remote  past  attest. 

Passing  by  the  many  improvements  in 
various  forms  of  oil  lamps,  perhaps  the 
next  noted  step  in  the  production  of  arti- 
ficial light  followed  in  the  discovery  of 
coal  oil,  and  marked  improvements  were 
made  in  lamps  designed  especially  to  burn 
this  natural  illuminant.  The  next  great 
improvement  in  this  direction  was  the 
lighting  of  extended  areas  by  means  of 
illuminating  gas.  Here,  for  the  first  time 
in  the  history  of  the  art,  means  were  de- 
vised for  supplying  an  illuminant  from  a 
central  station,  under  circumstances  which 
permitted  of  its  ready  distribution  over 
extended  areas. 

The  greatest  step,  however,  in  the  pro- 


4        ELECTRIC  INCANDESCENT  LIGHTING. 

duction  of  an  artificial  illuminant  was  un- 
doubtedly that  which  followed  the  inven- 
tion of  the  voltaic  pile  in  1796.  Then,  for 
the  first  time  in  the  history  of  science, 
means  were  provided  whereby  powerful 
electric  currents  could  be  readily  produced 
and  their  effects  observed.  Naturally  the 
use  of  these  currents  soon  led  to  the  dis- 
covery of  the  very  powerful  illuminating 
properties  possessed  by  the  voltaic  arc. 
It  must  not  be  supposed,  however,  that  in 
these  successive  steps  each  new  illuminant 
completely  supplanted  its  predecessors. 
On  the  contrary,  the  very  fact  that  night 
could  thus  be  transformed  into  day,  stimu- 
lated improvements  in  the  pre-existing 
forms  of  illuminants,  and,  in  the  emulation 
thus  produced,  marked  advances  were 
made  in  earlier  methods.  Thus,  it  was  at 
one  time  claimed,  when  gas  was  first  intro- 
duced into  cities,  that  existing  methods  of 


lighting  would  sot^  entirely  repla^ 
by  the  new  illummany'foj^ 
being  the  case,  old  methods  were  suffi- 
ciently improved  to  fairly  hold  their  own, 
and  even  to  require  continued  improve- 
ments in  the  new  illuminant,  in  order  to 
maintain  its  superiority.  So,  again,  when 
the  electric  light  was  introduced,  it  was 
predicted,  by  enthusiasts  that  gas  lighting 
would  now  be  entirely  replaced  by  its  new 
rival,  but,  as  is  well  known,  this  expec- 
tation was  not  realized.  So  markedly  have 
improvements  in  different  methods  of 
illumination  gone  hand  in  hand,  that  we 
possess  to-day  all  our  original  methods, 
save,  perhaps,  the  torch. 

Before  discussing  the  advantages  pos- 
sessed by  the  incandescent  electric  light,  it 
will  be  advantageous  to  consider  in  general 
the  requirements  of  any  artificial  illumi- 


6         ELECTRIC   INCANDESCENT   LIGHTING. 

nant.  It  is  evident  that  the  most  satis- 
factory artificial  illuminant  will  be  that 
whose  properties  most  nearly  resemble 
those  of  the  sunlight  it  replaces.  No 
existing  illuminant  completely  satisfies 
our  requirements  from  this  standpoint. 
The  ideal  artificial  illuminant  should 
possess  the  following  properties ;  it  should 
be, 

(1)  Safe. 

(2)  Cheap. 

(3)  Hygienic. 

(4)  Steady. 

(5)  Eeliable. 

(6)  Akin  to  sunlight  in  color. 

(7)  Capable  of  ready  subdivision. 

(8)  Cool. 

(9)  Readily  turned   on   and    off    at    a 
distance. 

(10)  Amenable  to  the  purposes  of  dec- 
oration. 


ARTIFICIAL   ILLUMINATION.  7 

As  regards  safety,  it  is  evident  that  an 
artificial  illuminant  should  be  safe  both 
to  property  and  to  life.  All  bare  or  naked 
flames  are  open  to  the  objection  that  com- 
bustible material,  coming  in  contact  with 
them,  may  start  dangerous  conflagrations. 

A  good  artificial  illuminant  must  neces- 
sarily be  cheap;  for,  unless  it  can  be  fur- 
nished a"t  a  price  which  brings  it  fairly 
within  the  reach  of  all,  its  use  will  be 
very  limited. 

All  artificial  illuminants  must  necessarily 
permit  of  continued  use  without  any  dele- 
terious eifects  on  the  health.  Such  defects 
may  arise  either  from  products  of  combus- 
tion vitiating  the  surrounding  air,  or,  possi- 
bly, in  extreme  cases,  from  injury  to  sight. 

Steadiness  is  a  prime  essential  of  a  good 


8         ELECTKIC   INCANDESCENT   LIGHTING. 

illuminant.  If  an  artificial  light  produces 
an  unsteady,  nickering  illumination,  an 
injurious  strain  may  be  put  on  the  eye,  in 
its  endeavor  to  accommodate  itself  to  the 
varying  intensity  of  illumination.  More- 
over, a  good  artificial  illuminant  must  be 
reliable.  In  other  words,  it  must  be  able 
to  furnish  light  without  constant  attention, 
and  without  danger  of  becoming  acciden- 
tally extinguished. 

Ordinary  sunlight,  as  is  well  known,  con- 
sists of  a  mixture  of  a  great  variety  of 
colors.  The  color  of  natural  bodies  is 
entirely  due  to  the  light  which  falls  on 
them.  For  example,  a  green  leaf,  illumined 
by  sunshine,  possesses  the  power  of  absorb- 
ing nearly  all  the  sunlight  but  the  green 
light,  which  it  gives  off.  For  such  a  green 
leaf  to  appear  of  its  natural  color  by  arti- 
ficial light,  this  light  must  possess  not  only 


ARTIFICIAL   ILLUMINATION.  9 

the  exact  tints  of  the  various  greens  which 
it  throws  off  in  sunlight,  but  also  the 
various  proportions  of  such  tints.  The 
same  is  true  for  other  colors.  A  good 
artificial  illuminant,  therefore,  to  be  able 
to  replace  sunlight,  should  possess  not  only 
all  the  colors  of  the  sunlight,  but  should 
also  possess  these  colors  in  nearly  the  same 
relative  intensities  as  does  sunlight. 

A  requirement  of  an  artificial  illum- 
inant, which  is  very  difficult  to  fulfil,  is 
that  the  light  it  produces  shall  not  be 
localized,  but  shall  uniformly  illumine  the 
spaces  to  be  lighted.  In  order  to  meet 
this  requirement,  the  artificial  illuminant 
must  readily  yield  itself  to  subdivision, 
that  is,  instead  of  giving  a  great  amount  of 
light  at  each  of  a  few  points,  it  should 
give  a  smaller 'quantity  of  light  at  a  great 
number  of  separate  points. 


10      ELECTRIC    INCANDESCENT   LIGHTING. 

The  light  of  all  artificial  illmninants 
is  accompanied  by  heat,  and,  in  nearly  every 
case,  the  amount  of  heat  so  accompany- 
ing the  light  is  very  greatly  in  excess  of 
what  is  essentially  necessary.  Such  is 
true  even  in  the  case  of  sunlight.  A  nota- 
ble exception,  however,  is  found  in  the 
phosphorescent  light  of  the  firefly  and  the 
glow-worm,  which  yield  light  practically 
devoid  of  wasteful  heat ;  i.  e.,  non-luminous 

Iwat. 

• 

Another  requirement  of  an  artificial 
illuminant  is  that  it  shall  readily  yield 
itself  to  control,  that  is  to  say,  that  it  shall 
easily  be  turned  on  or  off  at  a  distance, 
otherwise,  the  location  of  the  separate 
sources  of  light  would  necessarily  be 
limited  and  thus  prevent  the  most  advan- 
tageous distribution.  Finally,  a  good  arti- 
ficial illuminant  should  be  readily  adapta- 


ARTIFICIAL   ILLUMINATION.  11 

ble  to  the  purposes  of  decoration,  or 
it  will  otherwise  be  shorn  of  many  of  its 
advantages. 

The  principal  artificial  illuminants  in 
use  at  the  present  day,  are,  coal  oils,  gas, 
candles,  arc  and  incandescent  electric 

lamps. 

t 

The  incandescent  lamp  is  now  so 
generally  employed  as  an  indoor  artificial 
illuminant,  and  its  advantages  for  this 
purpose  are  so  evident,  that  it  is  scarcely 
necessary  to  show  how  much  more  fully  it 
meets  the  requirements  of  a  good  illuinin- 
ant  than  any  of  its  predecessors.  It  suffices 
to  say  that  it  does  not  vitiate  the  air,  is  re- 
liable, steady,  can  be  maintained  without 
any  trouble  on  the  part  of  the  consumer, 
and  readily  yields  itself  both  to  sub-division 
and  to  decorative  effects.  When  used  on 


12      ELECTRIC   INCANDESCENT   LIGHTING. 

a  comparatively  large  scale  it  can  compete 
favorably  as  regards  cost  witli  any  other 
artificial  illuininant,  and,  even  when  em- 
ployed on  a  small  scale,  its  manifold  advan- 
tages will  frequently  more  than  compensate 
for  the  disadvantage  of  a  slightly  increased 
cost. 

As  regards  the  ability  of  an  incandes- 
cent lamp  to  produce  a  color  of  light  akin 
to  sunshine,  it  must  be  confessed  that  it  is 
far  from  realizing  this  object,  but  this 
objection  also  exists  to  even  a  greater 
degree  in  nearly  all  other  artificial  illu- 
minants.  Coal  oil,  candles,  gas,  and  oil 
lamps  generally,  do  not  produce  a  light  so 
nearly  akin  to  sunshine,  as  does  the  incan- 
descent lamp.  As  we  shall  see  later  on 
the  light  emitted  by  an  incandescent  lamp 
can  be  made  to  approach  more  closely  the 
characteristics  of  sunlight  by  increasing 


ARTIFICIAL   ILLUMINATION.  13 

the    temperature  of    the  glowing  carbon 
filament. 

When  the  incandescent  electric  light 
was  first  introduced  on  a  commercial  scale, 
a  belief  existed  that  the  extended  intro- 
duction of  this  illuminant  would  be 
attended  by  many  dangers,  and  it  is  true 
that,  when  negligently  installed,  such 
dangers  do  exist,  but  experience  has  amply 
proved  that  when  installed  with  ordinary 
care,  there  is  far  less  danger  from  the  use 
of  incandescent  lighting  than  from  the  use 
of  any  other  artificial  illuminant. 

So  far  as  the  safety  of  incandescent 
lighting  for  fire  risk  is  concerned,  a  re- 
port of  the  Massachusetts  Insurance  Com- 
missioner, giving  data  extending  from  1884 
to  1889,  as  to  the  origin  of  12,935  confla- 
grations which  took  place  in  Massachusetts 


14      ELECTRIC   INCANDESCENT   LIGHTING. 

during  that  time,  will  speak  favorably  for 
this  illuminant.  Of  this  number  of  fires 
only  42  were  attributed  to  electric  wires. 
The  breakage  and  explosion  of  kerosene 
oil  lamps  produced  in  the  same  time  about 
22  times  as  many  fires,  while  the  careless 
use  of  matches  produced  more  than  10 
times  as  many. 

As  to  the  danger  to  life,  the  evidence  is 
still  more  in  favor  of  electricity  as  an  arti- 
ficial illuminant.  While  it  is  true  that 
fatal  accidents  do  occur  from  contact  with 
high-pressure  wires,  yet  the  proper  instal- 
lation of  a  system  practically  precludes  the 
possibility  of  such  accidents.  Besides  the 
immunity  from  fire  which  the  electric 
lamp  ensures,  owing  to  the  fact  that  the 
filament  is  sealed  in  a  glass  chamber,  thus 
preventing  contact  with  combustibles,  it 
also  possesses  the  marked  advantage  that 


ARTIFICIA 


it  dispenses  entire! ; 
dangerous  friction  matched 
readily  capable  of  being  lighted  and  ex- 
tinguished at  a  distance  by  the  mere  turn- 
ing of  a  switch.  To  thoroughly  appreciate 
the  danger  to  life  from  electricity,  and  to 
ascertain  the  extent  to  which  it  can  be 
avoided,  it  will  be  necessary  to  understand 
some  of  the  leading  elementary  principles 
of  electrical  science,  and  we  will,  there- 
fore, postpone  this  consideration  to  a  later 
chapter. 

An  extended  experience  with  the  incan- 
descent lamp,  has  clearly  established  its 
advantages  over  gas  or  coal  oil.  Take,  for 
example,  convenience  of  night  work,  in  a 
large  textile  manufactory.  It  is  a  well 
known  fact  that  the  air  of  such  buildings, 
when  illumined  by  gas,  so  rapidly  heats  and 
becomes  so  rapidly  vitiated  during  summer 


16      ELECTRIC   INCANDESCENT  LIGHTING. 

time,  that  the  amount  and  character  of  the 
work  the  workmen  are  capable  of  per- 
forming, necessarily  suffers  as  compared 
with  day  work.  Since  the  introduction  of 
the  incandescent  lamp,  however,  the  ab- 
sence of  increase  of  temperature  and 
impure  air,  on  prolonged  runs,  is  so  marked, 
that  in  many  instances  it  has  been  found 
that  the  amount  and  character  of  the  night 
work  compares  very  favorably  with  day 
work  during  the  summer  season.  This 
circumstance  has  frequently  occasioned 
surprise  to  the  public,  since  the  tempera- 
ture of  the  glowing  filament  in  an  incan- 
descent lamp  is  quite  high,  but  it  must  be 
remembered  that  while  an  incandescent 
lamps  emits  no  gas,  the  filament  not  being 
con  sinned,  a  gas  burner  not  only  gives  off 
all  the  gas  that  would  escape  from  it  were 
it  unlighted,  but,  in  addition,  a  much 
greater  volume  of  heated  air.  Every  cubic 


ARTIFICIAL   ILLUMINATION.  17 

foot  of  ordinary  illuminating  gas  requires 
for  its  combustion,  the  oxygen  from  about 
20  cubic  feet  of  air,  so  that  a  burner  con- 
suming 5  cubic  feet  per  hour  combines  with 
the  oxygen  of  about  100  cubic  feet  of  air 
per  hour.  Besides  vitiating  such  air  by 
the  products  of  combustion,  and  raising  its 
temperature  by  the  great  amount  of  heat 
given  off,  this  vitiation  and  increase  of 
temperature  requires  much  more  thorough 
ventilation  than  when  the  incandescent 
lamp  is  employed.  In  cases  where  the 
character  of  night  work  requires  keen 
sight,  a  highly  heated  vitiated  air  has  an 
injurious  influence  upon  the  eye. 


CHAPTER  II. 

EARLY  HISTORY    OF  INCANDESCENT   LIGHTING. 

ELECTRICITY  was  first  employed  as  an 
illuminant  in  the  arc  lamp.  In  this  lamp, 
as  is  well  known,  two  rods  of  carbon  are 
first  brought  into  contact,  and  then  gradu- 
ally separated  while  a  powerful  electric 
current  is  passing  between  them.  A 
cloud  of  incandescent  carbon  vapor,  called 
the  voltaic  arc  is  thus  established,  and  the 
ends  of  the  carbons,  particularly  that  of 
the  positive  carbon,  or  the  one  from  which 
the  current  flows,  becomes  intensely 
heated,  forming  a  brilliant  source  of  light. 

The  greatest  difficulty  attending  the 
practical  application  of  the  arc  system  of 

18 


EARLY   HISTORY.  19 

lighting,  arose  from  the  fact  that  the  arc 
lamp  was  too  intense  a  source  of  light  for 
most  practical  purposes  within  doors,  and 
could  not  readily  be  subdivided  into  a 
number  of  smaller  units ;  for,  even  if  the 
space  to  be  lighted  would  require  all  the 
light  emitted  by  a  single  arc  lamp,  yet 
this  light,  coming  from  practically  a  single 
point,  would  necessitate  the  production  of 
disagreeable  shadows. 

From  very  early  times  in  the  history  of 
the  application  of  electricity  to  lighting, 
the  idea  was  conceived  by  various  invent- 
ors of  employing  continuous  conductors, 
instead  of  the  discontinuous  conductors  in 
arc  lighting.  These  continuous  conductors 
were  rendered  incandescent  by  the  pas- 
sage through  them  of  an  electric  current ; 
or,  in  other  words,  the  current  heated 
them  to  a  white  heat.  Various  substances 


20      ELECTRIC   INCANDESCENT   LIGHTING. 

were  employed  for  this  purpose,  at  first  in 
air,  such  as  platinum  or  iridium  wires,  or 
other  metals.  These  lamps,  however,  were 
not  found  to  give  practically  useful 
results,  since  if  the  current  strength  was 
made  sufficiently  great  to  raise  them  to 
a  white  heat,  although  the  light  they 
would  then  emit  would  be  quite  satisfac- 
tory, yet  disintegration  would  occur,  from 
the  free  contact  of  the  air,  and  would  soon 
result  in  the  destruction  of  the  lamp. 
Moreover,  the  temperature  at  which  the 
glowing  wire  becomes  white  hot,  is  so 
very  nearly  the  temperature  of  its  melting 
point,  that  any  accidental  increase  in  the 
-current,  even  to  a  slight  degree,  would 
result  in  the  fusion  of  the  wire  and  the 
rupture  of  the  lamp.  If  to  avoid  these 
difficulties,  the  lamp  was  burned  at  a 
lower  temperature,  the  light  it  emitted 
was  unsatisfactory,  not  only  on  account  of 


EARLY    HISTORY.  21 

its  lessened  intensity,  but  also  because  it 
was  distinctly  red  and  dull. 

During  the  year  1878,  a  great  improve- 
ment was  effected  in  the  platinum  incan- 
descent lamp,  whereby  platinum  was  ob- 
tained in  a  condition  in  which  it  was 
possible  to  employ  safely  much  greater 
current  strength  without  rapid  deteriora- 
tion. This  process  consisted  essentially  in 
sending  a  gradually  increasing  current  of 
electricity  through  the  wire  while  in  a 
vacuous  space.  As  is  well  known,  plati- 
num possesses  in  common  with  some 
other  metals,  the  power,  of  absorbing  or 
occluding  within  its  mass,  air  or  other 
gases.  When  such  a  wire  is  heated  by  the 
sudden  passage  of  an  electric  current,  this 
occluded  gas  is  liberated  explosively,  and 
the  wire  thereby  becomes  cracked,  fissured, 
and  rapidly  disintegrates.  It  was  dis- 


22      ELECTRIC    INCANDESCENT   LIGHTING. 

covered  that  if  the  wire,  while  in  a  vacuous 
space,  was  subjected  to  the  passage  of  a 
gradually  increasing  current  of  electricity, 
first  beginning  with  a  weak  current,  that 
the  occluded  gas  was  slowly  liberated  and 
that  if,  when  a  very  high  vacuum  was  ob- 
tained, the  wire  was  maintained  for  a  few 
moments  at  a  temperature  only  a  little 
below  that  of  its  melting  point,  it  became 
physically  changed,  free  from  cracks  and 
had  its  point  of  fusion  raised.  Moreover, 
the  surface  of  the  wire  was  altered,  so  that 
a  given  current  strength  produced  a  greater 
amount  of  light.  The  invention  of  a  lamp 
consisting  of  such  a  treated  platinum  wire 
in  a  vacuous  space  was  a  marked  step  in 
the  production  of  an  artificial  electric  illu- 
niinant.  Nevertheless,  even  the  improved 
conductor  did  not  answer  commercial  re- 
quirements, so  that  the  improved  platinum 
lamp  did  not  come  into  any  extended  use. 


EARLY    HISTORY.  23 

To  make  the  incandescent  lamp  practi- 
cable it  was  necessary  to  enclose  the  wire 
in  a  transparent  chamber  from  which  the 
air  had  been  removed.  Such  an  improve- 
ment would  render  the  lamp  more  efficient 
for  the  following  reasons : 

(1)  The  absence  of  air  would  prevent 
the  rapid  disintegration  of  the  wire. 

(2)  The  absence  of  air  would  prevent 
the  re-absorption  or  occlusion  of  air  by  the 
heated  wire. 

(3)  The  absence  of  air  would  prevent 
loss  of  heat,  and  much  electric  power  would 
thereby  be  saved  since  a  smaller  current 
would  bring  the  wire  to  the  incandescent 
temperature. 

(4)  The  absence  of  drafts  of  air  would  pre- 
vent irregular  coolings  and  heatings  of  the 
wire,  with  consequent  fluctuations  of  light. 

(5).  The  wire  would  be  protected  from 
mechanical  injury. 


24      ELECTRIC   INCANDESCENT  LIGHTING. 

The  early  history  of  the  art  contains  the 
names  of  numerous  inventors  who  applied 
the  foregoing  principles  for  the  purpose  of 
producing  satisfactory  incandescent  lamps. 
Without  attempting  to  record  in  full  all 
these  early  attempts,  we  will  briefly  allude 
to  some  of  the  more  prominent  of  the  early 
inventors  in  this  field  of  artificial  illumina- 
tion. 

In  1841,  Frederick  De  Moleyn  patented 
in  England  a  process  for  the  production  of 
an  incandescent  lamp,  based  on  the  incan- 
descence of  platinum  wire  placed  inside  an 
enclosing  glass  chamber  from  which  the 
air  had  been  exhausted. 

In  1849  Petrie  produced  an  incandes- 
cent lamp  in  which  short  thin  rods  of 
indium,  or  its  alloys,  were  used  as  the  in- 
candescent material. 


EARLY   HISTORY.  25 

Considerable  excitement  was  created  in 
scientific  circles  in  France,  in  1858,  by  the 
announcement  to  the  French  Academy  of 
Sciences  by  one  of  its  members,  of  an 
improvement  in  incandescent  lamps  made 
by  one  De  Changy.  De  Changy  employed 
an  incandescent  platinum  lamp  of  the  form 
shown  in  Fig.  1,  in  which  a  wire  of  plati- 
num G ',  is  heated  to  incandescence  by  the 
passage  of  the  current  through  it.  The 
wire  was  enclosed  in  an  exhausted  glass 
vessel.  The  excitement  caused  by  this 
lamp  was  due  to  the  claim  made  by  De 
Changy  that  he  had  solved  the  problem  for 
the  successful  sub-division  of  the  electric 
light.  His  lamp  never  came  into  com- 
mercial use. 

The  great  improvement  in  lamps  of  this 
type  was  made  by  the  substitution  of 
carbon  wires  for  platinum  wires.  The 


26      ELECTRIC   INCANDESCENT   LIGHTING. 


FIG.  1. — DE  CHANGY'S  LAMP. 

honor  of  this  discovery  appears  to  be  due 
to  an  American  by  the  name  of  J.  W. 
Starr,  who  employed  plates  of  carbon 


EARLY   HISTORY.  27 

placed  inside  a  glass  vessel  containing  a 
Toricellian  vacuum.  Starr  associated  him- 
self with  an  Englishman  of  the  name  of 
King,  and  an  English  patent  was  obtained 
under  the  name  of  King.  It  is  from  this 
fact  that  the  Starr  lamp  is  not  infrequently 
alluded  to  in  literature  as  the  King  lamp, 
or  sometimes,  as  the  Starr-King  lamp. 
Starr  gave  a  successful  demonstration  in 
England  with  a  candelabra  of  26  of  his 
lamps,  the  number  of  States  then  in  the 
American  Union.  His  untimely  death, 
while  on  his  return  voyage  to  this  coun- 
try, retarded  the  progress  of  this  inven- 
tion. The  Starr-King  lamp  is  illustrated 
in  Fig.  2,  where  A,  is  a  rod  of  carbon 
clamped  at  its  extremities  to  the  rods  G  and 
J9,  and  situated  in  a  Torricellian  vacuum 
above  the  surface  of  mercury  in  a  barometer 
tube,  the  current  passed  through  the  rod  A 
raising  it  to  the  incandescent  temperature. 


28      ELECTRIC   INCANDESCENT   LIGHTING. 


FIG.  2.— STARR-KING  LAMP. 

The  next  invention  worthy  of  notice 
was  that  of  Lodygnine,  who  produced  a 
carbon  incandescent  lamp  in  1873.  This 
invention  was  deemed  by  the  St.  Peters- 


EARLY  HISTORY.  29 

burg  Academy  of  Sciences,  of  sufficient 
merit  to  warrant  the  award  of  a  special 
prize.  Lodyguine's  lamp  used  needles 
of  retort  carbon  terminating  in  blocks 
and  placed  inside  an  exhausted  glass 
globe.  In  practice,  in  order  to  avoid  the 
expense  of  exhausting  the  globe,  Lody- 
guine  sometimes  left  air  within  the  globe 
and  then  sealed  it  hermetically,  depending 
on  the  consumption  of  the  residual  air 
by  the  heated  carbons  to  produce  a  space 
devoid  of  oxygen.  This  form  of  vacuum, 
however,  was  not  found  suitable  for  com- 
mercial purposes.  Lodyguine's  lamp  was 
improved  by  Kosloff,  who  introduced 
modifications  for  the  supports  of  the 
carbon  pencils. 

In  1875,  Konn  produced  a  lamp  very 
similar  to  Lodyguine's.  Konn's  lamp  is 
shown  in  Fig.  3.  The  glass  globe  J3, 


30      ELECTRIC   INCANDESCENT   LIGHTING. 


FIG.  3.— KONN'S  LAMP. 


EARLY  HISTORY.  31 

closed  at  the  top,  rests  with  its  base  upon 
a  washer  of  soft  rubber  placed  in  the  lamp 
base,  and  pressure  is  brought  by  the  screw 
block  Z,  in  such  a  manner  as  to  maintain 
an  air-tight  joint.  The  lamp  was  ex- 
hausted through  the  orifice  K.  The 
metallic  base  formed  one  terminal  of  the 
lamp,  while  the  rod  D,  passing  through 
the  base  A,  in  an  insulating  tube,  formed 
the  other  terminal.  Between  the  terminals 
F  and  D,  were  two  rods  of  carbon,  so 
arranged  that  one  only  was  in  circuit  at 
any  one  time.  The  thinner  central  por- 
tion of  these  rods  was  heated  to  incan- 
descence by  the  electric  current  passed 
through  the  lamp,  while  the  thicker  por- 
tions O,  O,  served  to  cool  the  extremities, 
at  the  points  of  contact  with  the  support- 
ing frame.  After  the  first  rod  was  con- 
sumed, it  dropped  out  of  position,  and 
allowed  the  second  rod  to  replace  it.  When 


82      ELECTRIC   INCANDESCENT  LIGHTING. 


FIG.  4.— BOULIGUINE'S  LAMP. 


EARLY  HISTORY.  33 

the  second  rod  was  consumed,  the  lamp  be- 
came automatically  short-circuited.  The 
difficulty  with  this  lamp  was  the  too  rapid 
consumption  of  the  carbons. 

In  1876  an  improvement  was  made  by 
Boulyguine,  who  produced  a  lamp  intended 
to  obviate  this  difficulty.  In  Boulyguine's 
lamp,  the  carbon  is  automatically  fed 
upwards  as  it  consumes  away.  A  section 
of  this  lamp  is  shown  in  Fig.  4.  Here  the 
lower  holder  of  the  carbon  rod  has  a  slide 
in  which  guides  press  upwards  under  gravi- 
tational force,  and  feed  the  carbon  filament 
up  against  the  upper  electrode  as  the  short 
rod  or  filament  is  consumed. 

Fig.  5,  shows  a  form  of  Sawyer  lamp. 
Here  the  light-giving  medium  consists  of 
an  incandescent  carbon  pencil  at  the  top 
of  the  lamp.  This  consumes  away  slowly 


34      ELECTRIC   INCANDESCENT   LIGHTING. 


FIG.  5. — SAWYER'S  LAMP. 


EARLY   HISTORY.  35 

in  operation  at  its  contact  with  the  upper 
carbon  block,  at  the   rate  of  about   ^th 


FIG.  6.— FARMER'S  LAMP. 

inch  per  hour.  The  carbon  pencil  was 
about  eight  inches  in  length  and  was 
forced  upwards  as  consumption  took  place. 
The  lamp  was  mounted  in  a  glass  globe 
partially  exhausted. 


36      ELECTRIC   INCANDESCENT  LIGHTING. 

Fig.  6,  shows  an  early  form  of  carbon 
lamp  introduced  by  Farmer  in  1879. 
Here  a  short  horizontal  carbon  rod  is 
gripped  between  two  large  metallic  blocks 
in  the  exhausted  globe. 

All  the  lamps  we  have  hitherto  de- 
scribed have  proved  commercially  useless, 
in  the  forms  in  which  they  were  presented. 
What  might  have  been  the  effect  of  intro- 
ducing slight  modifications  into  such  lamps 
is  beyond  the  province  of  this  volume  to 
consider.  There  can,  however,  be  but 
little  doubt  that  the  want  of  a  cheap 
source  of  electric  current  stood  as  much 
in  the  way  of  the  progress  of  electric  in- 
candescent lighting,  as  any  glaringly  in- 
herent difficulty  in  the  structure  of  the 
lamps  themselves. 

Before  leaving  this  brief  history  of  the 


EARLY  HISTORY.  37 

early  forms  of  incandescent  lamps,  it  may 
be  well  to  discuss  some  of  the  many  forms 
that  were  devised  for  burning  in  the  open 
air.  These  lamps  strictly  speaking  were  of 
a  type  which  may  be  best  described  as  semi- 
incandescent  lamps.  They  operate  essen- 
tially on  the  principle  of  sending  a  current 
through  a  slender  rod  of  carbon  pressed 
against  a  block  or  larger  mass  of  the  same 
material.  Under  these  circumstances  the 
slender  rod  is  raised  to  intense  incandes- 
cence, especially  at  its  point  of  contact 
with  the  larger  electrode,  where,  in  reality, 
a  miniature  arc  is  formed.  Various  de- 
vices were  employed  in  lamps  of  this  type 
for  feeding  the  carbon  rod  or  pencil  as  it 
was  gradually  consumed.  In  some  lamps 
an  enclosing  glass  chamber  was  employed 
in  order  to  reduce  the  consumption  of  the 
carbon  as  far  as  possible.  This  type  of 
lamp  passes  insensibly  into  lamps  of  the 


38      ELECTKIC   INCANDESCENT   LIGHTING. 

purely  incandescent  form.  In  fact,  as  will 
be  observed,  some  of  the  preceding  lamps 
were  of  the  seini-incandescent  type. 


FIG.  7. — REYNIEB'S  LAMP. 


One  of  the  most  successful  of  the  early 
lamps  of  the  semi-incandescent  type  was 
that  of  Keynier.  In  the  Reynier  lamp  a 
movable  rod  of  carbon  C\  Fig.  7,  of  small 
diameter,  supported  as  shown,  rests  against 


EAEL' 


a  contact  block 

to  limit  the  incandesce 

lower  extremity,  a  lateral 


FIG.  8. — REYNIER'S  LAMP. 

is  kept  pressed  against  the  rod  <7,  by 
means  of  a  spring  R.  The  current,  there- 
fore, passes  through  the  lateral  contact 
piece  Z,  through  the  slender  rod  to  the 
contact  block  of  graphite  J5,  so  that  only 
the  portion  of  the  rod  between  these 


40      ELECTRIC   INCANDESCENT   LIGHTING. 

points  is  rendered  incandescent,  by  far  the 
greatest  amount  of  light  coming  from  the 
tip  or  extremity  J.  Fig.  8,  is  a  semi-dia- 
grammatic view  of  the  same  lamp  ar- 
ranged, however,  to  be  used  in  connection 
with  an  external  globe.  The  two  binding 
posts  at  the  top  of  the  lamp  form  its 
terminals.  No  vacuum  is  necessary  with 
this  form  of  lamp  since  the  slender  rod  of 
carbon  is  fed  downwards  as  the  point  con- 
sumes away. 

In  1878  an  Englishman,  named  Werder- 
mann,  took  out  a  patent  for  a  lamp 
founded  on  a  somewhat  similar  principle. 
In  the  Werdermann  lamp,  shown  in  Fig.  9, 
as  in  the  Reynier  lamp,  means  were  devised 
for  pressing  a  slender  carbon  rod  against  a 
fixed  electrode,  and  feeding  this  rod  up- 
wards as  it  consumed  away.  Werdermann 
employed  for  his  fixed  electrode  a  carbon 


EARLY  HISTORY.  41 

disc  and  advanced  a  slender  carbon  rod  by 
the  action  of  a  weight  or  counterpoise.  In 
order  to  avoid  the  casting  of  shadows 
downwards,  a  notable  defect  in  the 


FIG.  9. — WERDERMANN'S  LAMP. 

Reynier  lamp,  Werdermann  inverted  his 
lamps,  as  shown  in  the  figure.  Lamps  of 
the  combined  Reynier- Werdermann  type 
at  one  time  were  in  fairly  successful  practi- 
cal use,  and  formed  one  of  the  features 


42      ELECTRIC   INCANDESCENT   LIGHTING. 

of   the   Electrical   Exhibition   of  1881   at 
Paris. 

The  advent  of  the  really  successful  in- 
candescent lamp  dates  from  about  1879, 
and  from  this  year,  the  growth  of  the  in- 
candescent electric  lamp  industry  has  been 
extremely  rapid.  The  year  1879,  there- 
fore, marks  the  entrance  to  the  epoch  of 
contemporaneous  history,  into  which  we 
are  unable  to  enter  at  the.  present  time. 
We  will,  therefore,  close  this  extremely 
brief  history  of  the  art,  referring  the 
reader  for  further  particulars  to  contem- 
poraneous literature. 


CHAPTER  III. 

ELEMENTARY    ELECTRICAL    PRINCIPLES. 

THE  light  emitted  by  the  glowing  fila- 
ment of  an  incandescent  lamp  is  one  of  the 
effects  produced  by  the  passage  of  the 
electric  current  through  it.  Before  pro- 
ceeding to  a  discussion  of  the  operation 
of  the  incandescent  electric  lamp,  it  will 
be  necessary  to  consider  briefly  the  lead- 
ing elementary  principles  concerning  the 
production  and  flow  of  electricity. 

An  electric  flow  is  always  produced  by 

the  action  of.  what  is  termed  electromotive 

foi*ce,  generally  contracted  E.  M.  F.     No 

electric  source  produces  electricity  directly. 


44      ELECTRIC   INCANDESCENT  LIGHTING. 

What  is  produced  is  an  electromotive 
force,  and  an  E.  M.  F.,  in  its  turn,  pro- 
duces an  electric  current  when  permitted 
to  do  so.  Thus,  in  such  an  electric 
source  as  a  voltaic  battery,  an  E.  M.  F. 
is  produced,  and  this  independently  of 
whether  it  is  permitted  to  establish  an 
electric  current  or  not.  If  an  E.  M.  F.  be 
permitted  to  act,  it  will  invariably  establish 
an  electric  current.  In  order  to  do  this 
a  conducting  path  must  be  opened  to  it. 
Such  a  conducting  path  is  called  a  circuit. 

For  convenience,  it  is  universally  agreed 
to  regard  electricity  as  leaving  an  electric 
source  at  the  point  called  the  positive 
terminal  or  positive  pole,  and  re-entering 
the  source,  after  having  passed  through 
the  circuit,  at  a  point  called  the  negative 
terminal  or  negative  pole  /  that  is  to  say, 
electricity  is  regarded  as  flowing  from  the 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      45 

positive  to  the  negative  pole,  in  the  ex- 
ternal portion  of  the  circuit,  and  from  the 
negative  to  the  positive  pole,  in  the  internal 
portion  of  the  circuit,  that  is  within  the 
source. 

Since  all  electric  currents  are  due  in 
the  first  instance  to  the  action  of  an  E. 
M.  F.,  it  is  necessary  to  obtain  definite 
ideas  concerning  this  force.  E.  M.  F.  is 
to  electric  flow  the  analogue  of  ordinary 
pressure  to  the  flow  of  liquids  or  gases; 
that  is  to  say,  a  flow  or  current  never 
occurs  in  a  liquid  or  gas,  except  as  the 
result  of  difference  of  pressure  acting 
on  it,  and  the  liquid  or  gaseous  flow  is 
always  directed  from  the  point  of  higher 
pressure  to  the  point  of  lower  pressure. 
So  in  the  electric  circuit,  a  current  of  elec- 
tricity never  flows  unless  there  be  a  differ- 
ence of  electric  pressure,  or  an  E.  M.  F., 


46      ELECTRIC   INCANDESCENT   LIGHTING. 

and  the  electric  flow  is  always  directed 
from  the  point  of  higher  to  the  point  of 
lower  electric  pressure. 

E.  M.  F.  is  measured  in  units  called 
volts.  Thus,  a  voltaic  cell,  of  the  type 
known  as  a  Leclanche  cell,  has  an  E.  M.  F. 
of,  approximately,  1  1/2  volts.  Such  a 
cell  is  shown  in  Fig.  10.  A  carbon  plate 
CGC,  is  connected  to  the  positive  terminal 
JP,  while  a  rod  of  zinc  Z  Z,  is  connected  to 
the  negative  terminal  N.  This  cell  pro- 
duces, when  in  good  order,  an  E.  M.  F. 
of  about  1  1/2  volts,  even  when  on  open 
circuit,  that  is  when  the  terminals  jP,  and 
N,  are  disconnected  as  shown,  and  are, 
therefore,  producing  no  current.  If,  how- 
ever, these  terminals  be  connected  through 
a  conducting  path,  or  circuit,  a  current  of 
electricity  will  flow  under  the  pressure  of 
1  1/2  volts,  from  the  positive  terminal  jP, 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      47 

through  the  external  portion  of  the  circuit 
back  to  the  negative  pole  N,  and  from  the 


FIG.  10. — LECLANCHE  CELL. 

zinc  plate  through  the  solution  S  xSJ  to  the 
positive  terminal,  thus  completing  a  cir- 
cuital path. 


48      ELECTRIC   INCANDESCENT  LIGHTING. 

When  an  E.  M.  F.  greater  than  1  1/2 
volts  is  required,  from  cells  of  this  type,  a 
number  of  such  cells  are  so  connected  to- 
gether as  to  act  as  a  single  source.  Such  a 
combination  of  cells  is  called  a  battery.  If, 
for  example,  two  such  cells  be  joined  to- 
gether, with  the  negative  pole  of  one  cell 
connected  to  the  positive  pole  of  the  other, 
they  would  produce  a  battery  of  three  volts 
E.  M.  F.,  and  100  such  cells  connected  in 
this  way,  or  connected  in  series,  as  it  is 
called,  would  produce  a  battery  having 
a  total  E.  M.  F.  of  approximately  150 
volts. 

Voltaic  batteries  are  seldom  employed 
for  supplying  current  to  incandescent 
lamps  except  on  a  small  scale,  for  the 
reason  that  the  cost  of  the  current  so  pro- 
duced would  be  excessive.  In  almost  all 
cases  of  electric  lighting,  the  E.  M.  F.  is 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      49 

obtained  from  a  dynamo-electric  generator, 
a  machine  for  producing  electric  power 
by  the  expenditure  of  mechanical  power. 
Dynamo-electric  machines,  suitable  for 
incandescent  lighting,  will  be  considered 
in  a  subsequent  chapter. 

When  an  E.  M.  F.  is  permitted  to  act 
upon  a  closed  conducting  path  or  circuit, 
the  value  of  the  current  strength  produced 
therein,  that  is,  the  amount  of  electricity 
which  flows  in  a  given  time,  will  depend 
upon  two  circumstances ;  namely, 

(1)  Upon  the  value  of  the  E.  M.  F.; 
i.  e.j  the  number  of  volts. 

(2)  Upon    a    property    of    the    circuit 
called  its  electric  resistance,  that  is  to  say, 
the  opposition  it  offers  to  the  flow  or  pas- 
sage  of   electricity  through   it.     Thus,  if 
the  cell  shown  in  Fig.  10  has  an  E.  M.  F. 
of    1  1/2    volts,   and    produces    a    much 


50      ELECTRIC    INCANDESCENT   LIGHTING. 

greater  current  strength  in  fa  one  circuit 
than  in  another,  it  is  because  the  latter 
circuit  offers  a  greater  resistance  to 
the  flow  of  electricity  than  the  former. 
Some  idea  of  the  action  of  resistance,  in 
opposing  the  flow  of  electricity  in  an 
electric  circuit,  can  be  had  by  consider- 
ing the  analogous  case  of  the  flow  of  gas 
through  a  pipe  or  main.  A  long  narrow 
pipe  will  obviously  offer  a  greater  resist- 
ance to  the  passage  of  gas  through  it, 
from  a  reservoir,  than  a  larger  short  pipe. 

The  resistance  of  an  electric  circuit  is 
measured  in  units  of  electric  resistance 
called  ohms.  The  ohm  is  a  resistance  such 
as  is  offered  by  about  two  miles  of  ordinary 
overhead  trolley  wire,  or  about  one  foot  of 

very  fine  copper  wire,  No.  40  A.  W.  Gr.,  which 

3 
has  a  diameter  of  about  — Tth  inch. 


PROPERTY Of'; 

ELEMENTARY  ELECTI$fr$£  PRINCIPLES.      51  „> 


The  electric 

very  important  quantity. 
resistances   will,  therefore,  be  of  interest. 

An  ordinary  Bell  telephone  receiver  has 
a  resistance  of  about  75  ohms. 

An  ordinary  telegraph  sounder  has  a  re- 
sistance of  about  2  ohms. 

An  ordinary  incandescent  lamp,  of  16 
candle-power,  intended  for  11 5- volt  circuits, 
has  a  resistance,  when  lighted,  of  about 
250  ohms. 

The  electric  resistance  of  a  conductor 
depends  upon  its  length,  its  cross-sectional 
area,  and  upon  the  nature  of  the  material 
of  which  it  is  composed.  The  resistance 
increases  directly  with  the  length  of  con- 
ductor, and  inversely  as  the  cross-sectional 
area.  Thus,  if  a  mile  of  trolley  wire, 
weighing  1,690  Ibs.  has  a  resistance  of 
1/2  ohm,  two  miles  will  have  a  resistance 


52      ELECTRIC   INCANDESCENT   LIGHTING. 

of  one  ohm,  and  10  miles,  a  resistance  of  5 
ohrns.  If  the  above  trolley  wire  be 
doubled  in  cross-sectional  area,  and,  conse- 
quently, in  weight,  so  as  to  weigh  3,380  Ibs. 
per  mile,  its  resistance  will  be  only  1/4 
ohm  per  mile,  or  2  1/2  ohms  in  10  miles. 

The  resistance  of  wires,  each  a  mile  long, 
and  of  the  same  diameter  as  ordinary 
trolley  wire,  (0.325")  would  be  different 
with  different  materials.  Thus,  while  such 
-a  wire  of  copper,  has  a  resistance  of  about 
1/2  an  ohm,  an  iron  wire  of  the  same  size, 
length  and  diameter,  would  have  a  resist- 
ance about  6  1/2  times  greater,  or  about 
31/4  ohms,  and  when  of  lead,  about  12 
times  greater,  or  about  6  ohms.  Conse- 
quently, in  order  to  compare  the  relative 
resistance  of  wires  of  different  materials,  it 
is  necessary  to  refer  each  material  to  a  com- 
mon standard  of  dimensions.  This  is  done 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      53 

by  considering  the  resistance  of  a  wire 
having  unit  length  and  unit  cross-sectional 
area,  that  is  to  say,  the  resistance  of  a  wire 
having  a  length  of  one  centimetre  and  a 
cross-sectional  area  of  one  square  centi- 
metre. The  resistance  of  a  wire  with  such 
unit  dimensions  is  called  its  specific  resist- 
ance or  its  resistivity.  The  resistivity  of 
standard  soft  copper  is  1.594  microhms; 
i.  <?.,  1.594  millionths  of  one  ohm.  If  then 
a  wire  has  a  length  of  one  kilometre  (100,- 
000  centimetres)  and  a  cross-sectional  area 
of  1  square  centimetre,  it  would  have  a  re- 
sistance of  1.594  x  100,000  microhms  = 
1.594  X  100,000 

1,000,000         ai°94  ohm> at  the  tem- 

perature  of  melting  ice. 

The  resistivity  of  a  wire  is  the  scientific 
standard  for  comparing  its  resistance  with 
that  of  other  wires  of  the  same  length  and 


54      ELECTRIC   INCANDESCENT   LIGHTING. 

cross-sectional  area.  In  English-speaking 
countries,  where  the  centimetre  is  not  in 
general  use  as  the  unit  of  length,  the  stand- 
ard called  the  circular-mil-foot  is  very 
commonly  employed.  A  circular-mil  is 

the  area  of  a  wire  one  mil,  or 


an  inch,  in  diameter.  This  is  not  to  be 
confused  with  the  area  of  such  wire  ex- 
pressed in  square  inches.  The  number  of 
circular  mils  cross-sectional  area  in  any 
wire,  is  obtained  by  squaring  its  diameter 
in  mils.  Thus  a  wire  half  an  inch  in 
diameter,  would  be  a  wire  of  500  mils 
diameter,  and  the  number  of  circular  mils 
cross-sectional  area  in  such  wire  would 
be  500  X  500  =  250,000.  Such  a  wire 

would  have  a  resistance  per  foot  of  ^     ''    ^ 

250,000 

=  0.000,00414  ohm.  A  circular-mil-foot 
of  standard  soft  copper  at  20°  C.  has  a 
resistance  of  10.35  ohms. 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      55 

The  resistivity  of  a  material  varies  with 
its  temperature.  In  the  case  of  most  me- 
tallic substances,  the  resistivity  increases 
as  the  temperature  increases.  Thus,  the 
resistivity  of  copper  wire  is  about  forty- 
two  per  cent,  greater  at  the  boiling  point  of 
water,  than  at  its  freezing  point ;  or,  a  cop- 
per wire  would  have  about  forty-two  per 
cent,  more  resistance,  at  the  temperature  of 
the  boiling  point  of  water,  than  at  its  freez- 
ing point.  The  resistivity  of  insulating 
materials,  however,  diminishes  as  the  tem- 
perature increases.  Carbon  behaves  in 
this  respect  like  an  insulating  material,  its 
resistivity  diminishing  as  its  temperature 
increases.  An  ordinary  incandescent  lamp 
has  about  twice  as  much  resistance  when 
cold,  as  it  has  when  heated  by  the  electric 
current  to  an  incandescent  temperature. 

The     current     strength,  which     passes 


56      ELECTRIC   INCANDESCENT  LIGHTING. 

through  any  circuit,  is  measured  in  units 
of  electric  flow  called  amperes.  As  in  the 
case  of  a  current  or  flow  of  gas,  we  may 
estimate  the  flow  as  so  many  cubic  feet  of 
gas  per  minute,  or  per  second,  so  an  electric 
flow,  may  be  estimated  as  so  many  units 
of  electric  quantity  per  second.  The  unit 
of  electric  quantity  is  called  the  coulomb, 
and  is  the  quantity  of  electricity,  which 
would  flow  in  one  second  through  a  cir- 
cuit having  a  total  resistance  of  one  ohm, 
when  under  a  pressure  of  one  volt.  A 
rate  of  flow  equal  to  one  coulomb-per- 
second  is  the  unit  of  electric  flow  or  cur- 
rent, and  is  called  the  ampere.  A  current 
of  10  amperes,  therefore,  means  a  flow,  or 
transfer,  of  10  coulombs  of  electricity  in 
each  second.  The  ordinary  incandescent 
lamp  of  16  candle-power,  operated  at  a 
pressure  of  115  volts,  requires  to  be  sup- 
plied with  a  current  of  about  1/2  ampere. 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      57 

The  relations  existing  in  any  circuit 
under  a  given  resistance  and  E.  M.  F.  are 
readily  determined  by  reference  to  a  law 
discovered  by  Dr.  Ohin,  and  named  Ohm's 
Law.  This  law  may  be  expressed  briefly 
as  follows : 

The  current  strength  in  any  circuit  is 
directly  proportional  to  the  total  E.  M.  F. 
acting  in  the  circuit,  and  inversely  pro- 
portional to  tlie  total  resistance  in  the 
circuit. 

If  the  pressure  or  E.  M.  F.  be  measured 
in  volts,  and  the  resistance  in  ohms, 
the  current  strength  that  passes  in  am- 
peres may  be  briefly  expressed  as  follows: 

Volts 

Amperes  =  ^-r- 
Ohms 

For  example,  if  a  circuit  comprise  a 
dynamo  and  an  external  path  consisting 
of  lamps  and  wires,  so  that  the  E.  M.  F. 
in  the  dynamo  is  100  volts,  and  the  resist- 


58      ELECTRIC    INCANDESCENT   LIGHTING. 

ance    of  ..  the    circuit  is    2  olnns,  then  the 
current  strength  passing  through  the  cir- 

cuit will  be  -    -  =  50  amperes. 

a 

Again,  if  an  incandescent  lamp  has  a 
resistance  (hot)  of  220  ohms,  and  is  con- 
nected to  a  pair  of  mains  between  which 
the  electric  pressure  is  steadily  maintained 
under  all  circumstances  at  110  volts,  then 
the  current,  which  will  pass  through  the 

110        1 
lamp   irom   the   mains   will    be 

ampere. 


We  have  already  alluded  to  the  fact 
that  a  current  never  flows  in  water  unless  a 
difference  of  pressure  exists  therein.  In 
order  to  produce  this  difference  of  pressure, 
the  water  has  usually  to  be  raised  to  a 
higher  level  ;  and,  to  do  this,  energy  is  re- 
quired to  be  expended,  or  work  performed, 


f    PROPERTY  OF 


ELEMENTARY  ELECTK~  ~" 

on  the    water.     The 

tricity.  In  order  to  produce  an  electric 
flow,  energy  requires  to  be  expended,  or 
work  produced,  by  the  electric  source. 

Work  is  never  done  unless  force  acts 
through  a  distance.  A  force  that  is 
merely  producing  a  pressure  on  a  body, 
but  no  motion  of  the  body,  is  naturally 
performing  no  work.  When,  for  example, 
a  block  of  granite  is  raised  through  a 
vertical  distance  against  the  earth's  gravi- 
tational force,  work  is  done.  The  amount 
of  such  work  is  measured  by  the  force 
which  acts,  multiplied  by  the  distance 
through  which  it  acts.  For  example,  if 
a  block  weighing  200  pounds  be  raised 
through  10  feet,  an  amount  of  work  will 
be  done  expressed  in  a  common  unit  of  work 
called  the  foot-pound,  as  being  equal  to 
200  pounds  X  10  feet  =  2,000  foot-pounds. 


60      ELECTKIC   INCANDESCENT   LIGHTING. 

If  this  weight  when  raised  be  placed  on 
a  shelf  or  other  support,  it  would  still 
produce  a  pressure,  of  200  pounds  upon 
the  support,  but  would  be  doing  no 
work. 

Another  unit  of  work  is  called  the  joule, 
and  is  approximately  equal  to  0.738  foot- 
pound, so  that  a  foot-pound  is  about  thirty- 
five  per  cent,  greater  than  a  joule,  or  1 
foot-pound  =  1.356  joules.  A  man  weigh- 
ing 150  pounds,  and  raising  his  weight 
through  a  distance  of  100  feet  by  walking 
upstairs/  necessarily  performs  an  amount 
of  work  against  gravitational  force  equal 
to  100  X  150  =  15,000  foot-pounds  = 
20,340  joules. 

When  an  electric  current  passes  through 
a  circuit,  work  is  always  done  by  the  E. 
M.  F.  which  drives  the  current  through  the 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      61 

circuit.  The  amount  of  work  done  by 
the  E.  M.  F.  is  expressed  in  joules,  as  the 
product  of  the  pressure  and  the  quantity 
of  electricity  it  drives.  Thus,  if  a  quan- 
tity of  electricity  equal  to  100  coulombs, 
passes  through  an  electric  circuit  under 
a  pressure  of  50  volts,  then  the  amount 
of  work  which  will  be  expended  in 
the  passage,  will  be  50  X  100  =  5,000 
joules  =  3,690  foot-pounds.  A  joule  is, 
therefore,  equal  to  a  volt-coulomb.  This 
work  will  always  be  taken  from  the 
source  of  the  driving  E.  M.  F.  Thus  if 
the  dynamo  in  the  last  example,  supplied 
the  E.  M.  F.,  then  an  amount  of  work 
equal  to  5,000  joules  will  have  been  taken 
from  the  dynamo,  and  this  amount  of  work 
must  have  been  delivered  to  the  dynamo 
through  its  driving  belt.  Or,  if  the  E. 
M.  F.  had  been  supplied  by  a  voltaic 
battery,  this  amount  of  work  would  have 


62      ELECTRIC    INCANDESCENT   LIGHTING. 

been  supplied  at  the  expense  of  the  zinc  and 
the  liquid  in  the  battery ;  that  is  to  say  a 
certain  amount  of  zinc  would  have  been 
consumed,  thereby  liberating  at  least  5,000 
joules  of  work. 

It  is  necessary  to  distinguish  carefully 
between  the  amount  of  work  performed  in 
any  case  and  the  rate  at  which  such  work 
is  performed ;  for  example,  so  far  as  the 
result  attained  is  concerned,  the  same 
.amount  of  work  is  done,  when  the  man  be- 
fore alluded  to,  weighing  150  pounds,  raises 
himself  through  a  height  of  100  feet  by 
the  stairs,  whether  he  performs  this  work 
in  one  minute  or  in  ten  minutes,  but  his 
rate-of-doing-ioork,  or  his  activity  would  be 
10  times  greater  in  the  former  than  in  the 
latter  case.  In  the  former,  his  activity 
would  be  15,000  foot-pounds-per-minute, 
or  250  foot-pounds-per-second,  while  in  the 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      63 

latter  case  it  would  be  only  1,500  foot- 
pounds-per-minute,  or  25  foot-pounds-per- 
second.  Activity  is  commonly  rated  either 
in  terms  of  a  unit  of  activity  called  a 
foot-pound-per-second,  or  in  a  unit  called  a 
horse-power,  one  horse-power  being  equal  to 
550  foot-pounds-per-second,  or  33,000  foot- 
pounds-per-minute.  Thus,  in  the  preced- 
ing case,  the  man  would  be  expending  an 

250 
activity  of  -      =  0.455  horse-power  in  the 


first  case,  and  0.0455  horse-power  in  the 
second  case. 

Electric  activities  are  similarly  measured 
in  units  of  electric  power  or  activity  called 
watts,  the  watt  being  equal  to  an  activity 
of  a  joule-per-second,  or  a  volt-coulomb-per- 
second,  or  a  volt-ampere. 

Thus  if  a  current  of  1/2  ampere  passes 


64      ELECTRIC   INCANDESCENT  LIGHTING. 

through  an  incandescent  lamp  under  a 
pressure  of  115  volts,  the  electric  activity 
or  rate  of  expending  energy  in  the  lamp, 
will  be  115  x  1/2  =  57.5  watts,  or  joules- 
per-second  =  42.4  foot-pounds-per-second. 


CHAPTER  IV. 

PHYSICS      OF     THE     INCANDESCENT     ELECTRIC 
LAMP. 

BEFORE  proceeding  to  a  detailed  descrip- 
tion of  the  incandescent  lamp  and  the 
methods  employed  in  its  manufacture,  it 
will  be  advisable  to  obtain  a  general  in- 
sight into  the  physical  laws  controlling  its 
operation. 

Briefly  speaking,  the  operation  of  the 
incandescent  electric  lamp  is  based  upon 
the  principle  of  raising  the  temperature  of 
a  thin  thread  or  filament  of  some  refrac- 
tory substance,  such  as  carbon,  as  far  as 
is  consistent  with  practical  working.  In 


G5 


66      ELECTRIC   INCANDESCENT   LIGHTING. 

order  to  avoid  the  oxidation  of  the  carbon 
filament,  it  is  enclosed  in  a  glass  lamp  bulb 
in  which  a  vacuum  is  maintained.  Briefly, 
the  function  of  the  electric  lamp  is  to 
convert  electric  energy  economically  into 
.luminous  energy  or  light. 

Light  may  be  defined  in  two  distinct 
senses. 

First,  subjectively,  as  the  physiological 
effect  produced  through  the  eye  on  the 
mind  by  the  radiations  emitted  by  a 
luminous  body.  In  this  sense,  lights 
differ  in  their  color  and  intensity ;  that  is, 
we  are  conscious  of  different  perceptions 
both  of  color  and  of  intensity. 

Second,  objectively,  as  the  physical 
cause  which  produces  the  sensation  of 
light.  In  this  sense  light  can  have  an 
existence  independent  of  the  eye.  Objec- 
tively, light  consists  of  rapid  vibrations  or 


PHYSICS   OF  INCANDESCENT   LAMP.        67 

to-and-fro  motions  in  a  medium  called  the 
universal  or  luminiferous  ether,  which 
permeates  all  substances  and  spaces. 

The  luminiferous  ether  is  believed  to 
be  an  extremely  tenuous  and  highly  elastic 
medium,  which  not  only  fills  interstellar 
space,  but  which  even  permeates  the 
densest  forms  of  matter.  In  this  sense 
any  vibrations,  or  to-and-fro  motions,  of  the 
luminiferous  ether,  even  though  not  capable 
of  affecting  the  eye,  are  properly  spoken 
of  as  light,  but  of  course  the  light,  which 
it  is  the  function  of  the  incandescent  lamp 
to  produce  for  the  purposes  of  illumina- 
tion, must  necessarily  be  light  in  the 
physiological  sense. 

The  rapidity  of  the  oscillations  in  the 
ether  which  constitute  light  is  usually 
enormously  great.  This  frequency  has 


68      ELECTRIC   INCANDESCENT   LIGHTING. 

been  indirectly  measured  up  to  over  800 
trillions;  i.  e.,  over  800,000,000,000,000 
double  vibrations  per  second,  and  they 
may  exist  down  to  comparatively  low  fre- 
quencies, although  they  have  only  been 
measured  in  heat  radiation  as  low  as  about 
100  trillions  per  second.  Those  frequen- 
cies which  lie  between  390  trillions  and 
760  trillions,  are  capable  of  affecting  the 
normal  eye  as  physiological  light. 

All  bodies  emit  from  their  surfaces 
radiations  or  waves  into  surrounding  space. 
A  body  at  ordinary  temperatures  emits 
only  waves  of  a  comparatively  low  fre- 
qiiency,  far  below  that  which  is  capable 
of  affecting  the  eye  physiologically  as 
light.  As  the  temperature  of  the  body  is 
increased,  not  only  does  it  emit  these 
waves  of  low  frequency  more  powerfully, 
but,  in  addition,  it  also  emits  waves  of  a 


PHYSICS   OF   INCANDESCENT   LAMP.        69 

higher  frequency.  When  a  tempera- 
ture of  about  500°  C.  is  reached,  the 
highest  frequency  emitted  by  the  body 
will  be  just  about  390  trillions  of  double 
vibrations,  or  complete  to-and-f ro  motions, 
per  second,  and  will  be  just  visible  to  the 
eye.  The  body  is  then  said  to  be  at  the 
temperature  of  dull  red.  As  the  tempera- 
ture is  still  further  increased,  the  total 
radiation  of  waves  from  the  surface  in- 
creases, and  at  the  same  time  higher  fre- 
quencies are  introduced.  These  affect  the 
eye  successively  as  orange,  yellow,  green, 
blue,  indigo  and  violet ;  and,  finally,  all 
these  colors  being  present,  the  body  is 
said  to  be  white  hot,  and  has  a  tempera- 
ture of  roughly  1,500°  C.  If  the  tempera- 
ture be  still  further  increased,  the  lumi- 
nous intensity ;  i.  e.9  the  amount  of  visible 
radiation  per  unit  area  of  its  surface,  will 
increase,  and  at  the  same  time  still  higher 


70      ELECTRIC   INCANDESCENT   LIGHTING. 

frequencies  will  be  introduced  into  these 
vibrations,  which  are  necessarily  invisi- 
ble to  the  eye.  These  are  called  ultra- 
violet rays,  or  those  rays  above  the 
violet. 

If  we  analyze  sunlight,  we  will  find  that 
it  contains  all  frequencies  from  the  lowest 
that  we  can  measure  up  to  the  ultra-violet. 
The  greatest  intensity  of  these  vibrations 
falls  within  the  limits  of  the  invisible  fre- 
quencies, only  about  thirty  per  cent,  of  the 
vibrations  which  we  receive  at  the  earth's 
surface  being  capable  of  affecting  the  eye. 
The  visible  frequencies  combine  to  pro- 
duce on  the  eye  an  impression,  known  as 
white  light.  In  other  words  we  judge  a 
luminous  body  as  white,  when  it  emits 
frequencies  of  the  character  and  general 
proportions  which  exist  in  sunlight,  or  the 
relative  proportions  of  red,  green,  yellow, 


PHYSICS   OF   INCAN 

and  blue  frequencies  or 
the  same  in  this  light  as  in 

Generally  speaking,  nearly  all  sources  of 
artificial  light  emit  frequencies  which  are 
the  same  as  those  in  sunlight,  but  the 
amount  of  radiation  in  the  different  fre- 
quencies or  colors  varies  markedly  from 
sunlight.  Thus  a  candle  while  emitting 
all  the  visible  frequencies  of  sunlight 
has  a  marked  preponderance  of  red  rays 
relative  to  the  number  of  violet  rays, 
and  consequently  has  a  reddish  yellow 
tint. 

The  color  of  a  body  depends  upon  two 
things ;  viz. ,  first  upon  the  quality  of  the 
light  it  receives,  that  is  upon  the  propor- 
tionate distribution  of  the  various  frequen- 
cies, and  second  upon  the  selective  proper- 
ties of  its  surface.  When  light  falls  on  a 


72      ELECTEIC   INCANDESCENT  LIGHTING. 

colored  body,  the  surface  of  the  body  pos- 
sesses the  power  of  absorbing  some  of  the 
frequencies  and  throwing  off  others  unab- 
sorbed.  Thus,  a  blue  body,  illumined  by 
sunlight,  absorbs  practically  all  the  frequen- 
cies except  those  of  the  blues,  which  it  emits. 
For  the  blue  body  to  be  visible  in  its  proper 
tint,  therefore,  it  is  necessary  that  the  light 
which  illumines  it  shall  not  only  contain 
blues,  but  shall  also  contain  the  same  pro- 
portionate quantities  of  the  different  tints 
of  blue  as  sunlight.  If  these  colors  be  not 
present  in  the  artificial  light,  such  a  blue 
body  would  fail  to  possess  its  character- 
istic daylight  color-value.  Consequently, 
an  artificial  illuminant,  in  order  to  replace 
sunlight  for  the  purpose  of  revealing  the 
proper  daylight  color-values  of  bodies, 
must  contain  not  merely  the  same  fre- 
quencies as"  sunlight,  but  also  the  same 
relative  distribution  of  such  frequencies. 


PHYSICS   OF  INCANDESCENT   LAMP.        73 

All  light  serves  either  to  distinguish  the 
form  and  shape  of  bodies,  or  their  colors. 
For  the  latter,  as  we  have  seen,  an  approx- 
imate imitation  of  sunlight  is  necessary; 
for  the  former,  almost  any  frequency  of 
light  will  be  sufficient.  For  example,  if 
differently  colored  bodies  be  observed  in 
a  dark  room,  by  means  of  an  artificial 
light  containing  practically  but  one  fre- 
quency, and  called  usually  a  monochro- 
matic light,  only  the  color  of  this  light 
will  be  visible,  all  other  colored  objects 
will  appear  black,  or  devoid  of  color.  A 
yellow,  monochromatic  light,  may  be  ob- 
tained, for  example,  by  the  burning  of 
alcohol  on  a  wick  soaked  in  common  salt. 
In  the  pure  yellow  light  this  emits,  all 
yellow  colored  objects  will  appear  in 
nearly  their  true  tints,  while  the  reds, 
blues,  greens,  and  other  tints  will  appear 
devoid  of  color.  All  objects,  however, 


74      ELECTRIC   INCANDESCENT   LIGHTING. 

whatever  their  color,  will  show  their  form 
even  when  so  illumined. 

The  light  emitted  by  an  incandescent 
electric  lamp  is  not  capable  of  giving  true 
sunlight  color-values.  An  analysis  of  the 
light  from  the  glowing  filament,  shows  a 
relative  preponderance  of  red  and  yellow 
rays  and  a  deficiency  of  the  blue  and 
violet,  or  high-frequency  waves.  This  is 
owing  to  the  fact  that  the  temperature 
of  the  glowing  filament  cannot  be  raised 
sufficiently  high  to  emit  the  sunlight  pro- 
portions of  the  higher  frequencies.  Con- 
sequently, reds  and  yellows,  viewed  by 
incandescent  lamp  light,  give  nearer  ap- 
proach to  their  sunlight  values  than  other 
colors.  It  is  true  that  by  raising  the 
temperature  of  the  carbon  filament  we 
obtain  a  closer  approach  to  sunlight  radia- 
tion, but,  at  the  same  time,  for  reasons 


PHYSICS   OF   INCANDESCENT   LAMP.        75 

which    will    be    subsequently    explained, 
the  life  of   the  lamp  is  greatly  shortened. 

A  hot  body  loses  its  heat  in  one  of  four 
ways ;  viz.,  by  radiation,  by  conduction, 
by  convection  and  by  molecular  transfer. 

Were  the  glowing  filament  in  an  abso- 
lutely vacuous  space,  it  is  evident  that  being 
supported  on  a  comparatively  slender 
base,  apart  from  the  trifling  loss  of  heat 
through  this  base  or  support  there  would 
be  no  other  means  for  losing  the  heat  save 
by  radiation.  Once  admitting  within  the 
lamp  chamber  even  a  minute  trace  of  gas 
such  as  would  make  the  pressure  one- 
millionth  part  of  that  in  the  atmosphere, 
then  pure  radiation  would  cease  to  form 
the  sole  means  of  losing  heat,  and 
molecular  transfer  would  begin  to  act. 
That  is  to  say  the  air  molecules  coming 


76      ELECTRIC   INCANDESCENT   LIGHTING. 

into  contact  with  the  heated  filament 
would  be  shot  off  from  its  surface  in 
straight  paths,  and,  in  a  highly  attenuated 
atmosphere,  the  molecules  would  nearly 
all  fly  to  the  chamber  walls  without 
mutual  collision.  Heat  energy  is  required 
to  produce  this  motion,  and  the  loss  of 
energy  so  occasioned  forms  an  additional 
means  whereby  a  heated  body  in  a  rarified 
atmosphere  parts  with  its  heat. 

As  more  air  is  admitted  to  the  interior 
of  an  exhausted  lamp,  the  collisions  of  the 
air  molecules,  flying  from  the  heated  surface, 
become  more  frequent,  and  the  frequency 
with  which  they  are  returned  to  the  hot 
surface  also  increases,  increasing  thereby 
the  loss  of  heat  by  molecular  transfer.  As 
soon,  however,  as  the  mean  free  paths,  or 
uncollided  path,  of  the  molecules  becomes  a 
small  fraction  of  the  distance  between  the 


PHYSICS   OF  INCANDESCENT  LAMP.        77 

filament  and  the  wall  of  the  chamber, 
the  frequency  with  which  the  molecules 
return  to  be  shot  off  from  the  hot  surface 
increases  very  slowly,  so  that  beyond  this 
point  there  is  scarcely  any  increase  in  loss 
of  heat  by  molecular  transfer  as  air  is 
admitted  into  the  chamber.  As  more  air 
is  gradually  admitted  into  the  chamber, 
however,  the  loss  by  simple  convection 
increases,  i.  e.,  by  a  thermal  stirring  of  the 
air  owing  to  differences  of  density,  or  local 
winds,  within  the  lamp  chamber. 

The  radiation  emitted  by  the  ordinary 
incandescent  electric  lamp  is  principally 
non-luminous;  that  is  to  say  the  greater 
portion  possesses  a  frequency  below  the 
inferior  limit  of  visibility.  An  ordinary 
16-candle-power  lamp  has  an  activity, 
when  in  operation,  of  about  50  watts. 
Of  this  activity  about  48  watts  are  ex- 


78      ELECTRIC    INCANDESCENT   LIGHTING. 

pended  in  non-luminous  radiation,  and 
only  about  2  watts,  or  four  per  cent.,  in 
luminous  radiation.  The  problem  that  still 
remains  to  be  solved  in  the  incandescent 
lamp,  as  it  does  indeed  in  the  case  of  all 
artificial  illuminants,  is  to  produce  a  radia- 
tion which  shall  lie  wholly,  or  almost 
wholly,  between  the  limits  of  visible  fre- 
quencies. As  it  exists  to-day,  in  the  case 
of  the  incandescent  lamp,  the  energy  is 
expended  in  producing  about  ninety-six 
per  cent,  of  objectionable  heat  radiation, 
and  four  per  cent,  of  light  radiation.  Even 
this,  however,  has  a  luminous  efficiency 
superior  to  that  of  gas  and  oil. 

It  has  been  found  that  the  light  emitted 
by  the  firefly  and  the  glow-worm  is  prac- 
tically confined  to  the  visible  limits  of 
frequency.  Could  an  incandescent  lamp 
be  made  to  restrict  its  radiation  to  such 


PHYSICS   OF   INCANDESCENT   LAMP.        79 

frequencies,  the  problem  of  cheap  light 
might  be  solved.  Unless,  however,  such 
light  could  be  made  to  possess  these  fre- 
quencies in  sunlight  proportions,  it  is 
question  able  whether  the  problem  of  an 
efficient  illuminant  would  be  solved  from 
the  color  standpoint. 

Passing  by  the  question  of  the  produc- 
tion of  lamps  which  shall  yield  fre- 
quencies characteristic  of  the  light  of  the 
firefly  and  glow-worm,  there  would  appear 
to  remain  but  one  direction  in  which  the 
same  result  might  be  reached;  namely, 
by  obtaining  a  substance  which  possessed 
marked  powers  of  selective  radiation  ;  that 
is,  a  high  ability  to  radiate  waves  of  high 
frequency,  and  but  little  for  radiating 
those  of  low  frequency. 

When  an  electric  current  is  sent  through 


80      ELECTRIC   INCANDESCENT   LIGHTING. 

the  filament  of  an  incandescent  lamp,  the 
activity  expended  in  the  lamp  will  be  the 
product  of  the  pressure  at  the  lamp  termi- 
nals in  volts,  and  the  current,  in  amperes, 
passing  between  them.  This  activity  will 
be  entirely  expended  as  heat  in  the  sub- 
stance of  the  filament,  and  this  heat  will 
be  liberated  from  the  surface  in  virtue  of 
the  increase  of  temperature  of  that  surface. 
As  the  amount  of  heat  liberated  in  the 
filament  increases ;  i.  e.,  as  the  current 
strength  passing  through  it  increases,  the 
temperature  of  the  filament  is  compelled 
to  rise  in  order  to  emit  the  activity  which 
is  developed  in  its  mass.  If  the  surface  of 
the  filament  be  large,  it  will  take  a  large 
total  amount  of  activity  in  the  lamp  to 
maintain  a  large  radiation  per  square 
inch,  or  per  square  centimetre ;  whereas, 
if  the  surface  of  the  filament  be  small,  the 
opposite  result  will  be  produced.  Con- 


PHYSICS  OF  INCANDESCENT  LAMP.       81 

sequently,  a  certain  relation  must  exist 
between  the  surface,  the  length,  and  the 
cross  section  of  the  filament,  in  order  that, 
at  the  pressure  intended  for  the  circuit, 
the  radiation  per  square  inch,  or  per  square 
centimetre,  shall  be  sufficient  to  bring  the 
lamp  to  the  proper  temperature.  The 
nature  of  the  surface  of  the  filament  deter- 
mines, to  a  great  extent,  the  character  and 
amount  of  the  radiation  which  it  will  emit. 
It  might  be  supposed  that  the  same  activity 
per  square  centimetre  of  surface  would  be 
attended  by  the  same  temperature  and  rela- 
tive distribution  of  vibration  frequencies. 
Such,  however,  is  not  the  case,  the  charac- 
ter of  the  surface  having  a  marked  influ- 
ence upon  its  emissivity,  one  type  of  carbon 
producing,  with  a  given  activity  of  sur- 
face, a  greater  amount  of  light  than  another. 

The  temperature  at  which  ordinary  in- 


82      ELECTRIC   INCANDESCENT  LIGHTING. 

candescent  lamp  filaments  are  operated, 
is  estimated  at  about  1,345°  C.  If  this 
temperature  be  'exceeded,  by  only  a  few 
degrees,  although  the  candle-power  of  the 
filament  will  be  materially  increased,  yet 
the  disintegration  of  the  carbon,  by  a 
process  akin  to  evaporation,  will  be  rap- 
idly brought  about.  Thus,  an  increase  of 
2°  C.  is  believed  to  be  accompanied  by 
an  increased  candle-power  of  about  three 
per  cent.,  but  this  gain  is  at  a  marked 
decrease  in  the  life  of  the  lamp. 


^nw 


PROP, 


'ffry  OF 


\ki<V 


CHAPTER  V. 

MANUFACTURE  OF  INCANDESCENT  LAMPS. 
PREPARATION  AND  CARBONIZATION  OF 
THE  FILAMENT. 

THE  most  important  step  to  be  taken 
in  the  manufacture  of  an  incandescent  elec- 
tric lamp  is  the  preparation  of  the  fila- 
ment. Of  all  substances  which  have  been 
employed  for  filaments,  carbon  alone  has 
been  found  to  meet  the  requirements  of 
use.  In  the  first  place,  carbon  is  highly 
refractory ;  that  is,  capable  of  withstand- 
ing a  high  temperature  before  reaching  its 
point  of  volatilization.  In  the  next  place, 
its  resistivity  is  high,  so  that  a  high  resist- 
ance can  be  readily  given  to  a  short  length 


84      ELECTRIC   INCANDESCENT  LIGHTING. 

of  filament,  with  a  correspondingly  high 
electric  pressure  at  the  terminals,  for  a 
given  activity  in  the  lamp. 

Carbon  is  universally  employed  for 
lamp  filaments,  not  only  for  the  reasons 
above  pointed  out,  but  because  this 
material  readily  lends  itself  to  being 
fashioned  and  shaped  into  the  filament,, 
prior  to  being  subjected  to  various  proc- 
esses of  carbonization,  intended  to  ensure 
a  nearly  pure  form  of  hard  high-resisting 
carbon. 

A  great  variety  of  materials  have  been 
employed  for  producing  the  carbon  fila- 
ments of  incandescent  lamps.  All  these 
substances  agree  in  that  they  are  of  such  a 
nature  as  will  yield  a  nearly  pure  carbon 
when  subjected  to  carbonization,  i.  e.,  to 
the  action  of  heat  while  out  of  contact 


PREPARATION   OF   THE   FILAMENT.         85 

with  air.  Substances  suitable  for  this  pur- 
pose may  be  divided  into  two  sharply 
marked  classes ;  namely, 

(1)  Carbons  of  fibrous  origin,  such  as 
bamboo. 

(2)  Structureless  carbons,  such  as  pastes 
or  mixtures  of  finely  ground  carbon  incorpo- 
rated with  some  suitable  carbonizable  liquid. 

Among  substances  of  fibrous  origin,  that 
have  been  employed  for  incandescent  fila- 
ments, may  be  mentioned  paper,  bamboo, 
bass  fibre,  cotton  thread,  and  silk  thread, 
both  of  the  latter  substances  being  first 
subjected  to  a  process  which  is  called  the 
parchmentizing  process,  by  treatment  with 
sulphuric  acid.  Cellulose,  treated  in  such 
a  manner  as  to  be  converted  into  a  variety 
of  gun-cotton  and  subsequently  carbonized, 
has  also  been  employed.  This  material, 
although  of  fibrous  origin,  would  by  its 


86      ELECTRIC   INCANDESCENT   LIGHTING. 

treatment  be  rendered  capable  of  classifica- 
tion as  structureless  material.  Without 
here  entering  into  a  full  description  of  the 
various  processes  required  for  the  manu- 
facture of  filaments  from  the  above 
materials,  it  will  suffice  to  describe  in 
detail  the  process  adopted  in  a  few  cases. 

In  the  manufacture  of  a  bamboo  fila- 
ment, carefully  selected  bamboo  is  em- 
ployed, from  which  both  the  softer  por- 
tions in  the  interior,  and  the  hard  silicious 
parts  near  the  surface,  have  been  removed. 
The  material  is  then  cut  or  fashioned,  by 
the  aid  of  a  cutting  tool,  into  filamentary 
strips,  care  being  taken  to  obtain  as  nearly 
as  possible  the  same  area  of  cross  section 
by  passing  the  filaments  through  gauges. 
The  filaments  so  prepared  are  then  con- 
verted into  hard  carbon  by  means  of  a  car- 
bonizing process. 


PREPARATION    OF  THE   FILAMENT.         87 

In  the  production  of  a  filament  from 
loosely  spun  pure  cotton,  the  thread  is  first 
cleansed  from  grease  by  boiling  in  soda  or 
ammonia,  this  cleansing  being  necessary  for 
ensuring  uniformity  of  action  on  the  part 
of  the  sulphuric  acid  used  in  a  subsequent 
process.  The  thread  is  then  thoroughly 
washed  in  water  and  afterward  soaked  in 
sulphuric  acid  of  specific  gravity  1.64. 
The  time  of  immersion  is  exceedingly 
short,  varying  with  the  thickness  and  char- 
acter of  the  thread,  from  three  to  fifteen 
seconds.  On  removal  from  the  acid,  the 
thread  is  'again  washed  in  water.  After 
removal  from  the  water,  care  must  be 
taken  to  avoid  warping.  The  dried  thread 
in  this  condition  has  the  appearance  of 
catgut  and  is  called  amyloid. 

The  parchmentized  thread  has  a  rough 
surface,  and  is  too  irregular  in  diameter  to 


88      ELECTRIC   INCANDESCENT   LIGHTING. 

permit  it  to  be  subjected  in  this  condition 
to  the  carbonizing  process.  In  order  to 
ensure  uniformity  in  its  diameter,  and 
smoothness  of  its  surface,  it  is  passed 
through  a  series  of  draw  plates,  until  a 
sufficient  amount  has  been  removed  from 
it  to  permit  the  cutting  tool  to  act  on  all 
portions  of  its  surface.  These  draw  plates 
are  made  either  of  steel,  or  of  jewels,  the 
latter  being  the  most  frequently  employed. 
The  thread  so  produced  is  then  subjected 
to  the  carbonizing  process. 

Another  process,  which  also  produces  an 
amyloid  thread  from  pure  cellulose,  is 
sometimes  employed.  Here  pure  cellulose 
is  dissolved  at  a  temperature  of  about  the 
boiling  point  of  water,  in  zinc  chloride  of 
specific  gravity  1.8.  The  viscous  mass  so 
obtained  is  then  forced  or  squirted  under 
pressure  through  a  die  of  suitable  diameter 


PREPARATION    OF   THE   FILAMENT.         89 

into  a  vessel  containing  alcohol,  which 
causes  a  hardening  of  the  filament.  If 
this  process  is  properly  carried  on  it  pro- 
duces a  filament  of  uniform  cross-sectional 
area,  so  as  to  dispense  with  the  necessity 
for  passing  the  thread  through  shaving 
dies.  Care  has  to  be  taken  to  avoid  the 
formation  of  air  bubbles  in  the  viscous 
mass,  which  would  either  result  in  a  break- 
ing of  the  thread,  or  in  a  lack  of  homo- 
geneity of  the  filament.  This  process  is 
now  in  very  extensive  use. 

Another  process  has  been  invented  for 
the  production  of  an  artificial  material 
suitable  for  cutting  or  shaping  into  fila'ments 
for  incandescent  lamps,  and  subsequent  car- 
bonization. This  process  consists  essen- 
.tially  in  converting  cellulose,  obtained  from 
cotton,  into  a  substance  known  as  pyroxy- 
liue,.,or  gun-cotton,  whence  it  is  converted 


90      ELECTRIC   INCANDESCENT  LIGHTING. 

into  celluloid.  The  celluloid  is  rolled  into 
thin  sheets.  The  sheets  in  this  condition 
are  not  yet  fit  to  be  subjected  to  the  car- 
bonizing process,  and  must  first  be  again 
converted  into  cellulose.  This  change  is 
effected  by  treating  them  with  am- 
monium sulphide,  which  produces  struc- 
tureless, cellulose  sheets.  These  are  then 
treated  with  bisulphide  of  carbon,  or  tur- 
pentine, to  remove  all  traces  of  sulphur, 
and  are  then  ready  to  be  cut  or  shaped 
into  filaments  and  carbonized. 

The  filaments  so  cut  or  shaped  by 
the  preceding  processes,  must  be  sub- 
jected to  a  carbonizing  process.  During 
carbonization  a  number  of  changes  occur 
in  the  filament.  In  the  first  place  the 
filament  becomes  hard  and  brittle,  and, 
to  a  certain  extent,  acquires  a  definite 
shape  or  form,  so  that  it  is  necessary  be- 


PROPERTY  CF 

91 


PREPARATION 

fore  carbonizing  it 
which  it  is  to  permanently  retain.  In 
the  next  place  the  filament  shrinks  per- 
ceptibly during  carbonization,  so  that 
means  must  be  devised  for  permitting 
this  shrinking  to  take  place  without 
rupture. 

The  means  employed  for  the  carboniza- 
tion of  the  filament,  will  vary  with  the 
shape  and  character  of  the  material  of 
which  it  is  made.  The  degree  and  dura- 
tion of  the  heat  employed  in  carbonization 
will  also  vary  with  the  character  and 
method  of  preparation  of  the  material. 
It  will,  therefore,  be  necessary  briefly  to 
describe  the  methods  employed  for  the 
carbonization  of  particular  characters  of 
filaments.  In  this  connection,  however, 
it  must  be  remarked  that  the  manufac- 
ture of  the  incandescent  lamp,  as  it  is 


92      ELECTRIC    INCANDESCENT   LIGHTING. 

carried  out  to-day,  is,  to  a  great  extent, 
a  secret  process.  Therefore,  such  descrip- 
tions must  necessarily  be  limited  to 
known  processes  which  have  been  tried 
and  which  have  been  found  successful  in 
practice. 

In  the  case  of  the  bamboo  filaments,  the 
material,  shaped  as  already  described,  is 
placed  in  a  suitable  box  or  receptacle 
formed  of  carbon,  or  other  refractory  sub- 
stance, under  such  conditions  that  the  fila- 
ment shall  be  permitted  to  contract  freely 
while  being  subjected  to  a  constant  and 
even  tension.  In  Fig.  11,  such  a  box  is 
shown  with  the  filaments  to  be  carbonized 
placed  in  position.  This  box  is  in  two 
parts  as  shown,  an  outer  air-tight  chamber, 
and  an  inner  forming  plate.  The  fila- 
ments to  be  carbonized  are  placed  in  the 
inner  groove  around  the  block  E II,  with 


PREPARATION    OF    THE   FILAMENT. 


93 


their  extremities  secured  beneath  the 
bridge  piece  a  h,  which  is  fixed  in  an 
outer  frame.  As  the  filaments  contract 


FIG.  11.— CARBONIZING  Box. 

during  the  process,  since  they  cannot 
draw  up  into  the  groove  from  the  bridge, 
they  pull  the  whole  block  EH,  forward 
under  the  bridge,  and  so  maintain  a  steady 


94      ELECTRIC   INCANDESCENT   LIGHTING. 

and  uniform  tension  upon  the  filaments. 
A  suitable  cover,  provided  with  a  flange 
fitting  into  the  outer  groove,  is  placed  on 
the  box.  A  number  of  such  boxes  are 
packed  together  into  a  suitably  closed  flask 
which  is  placed  in  the  carbonizing  furnace. 

When  the  filaments  to  be  carbonized 
are  prepared  from  cotton  thread,  by  the 
process  already  described,  owing  to  the 
pliability  of  the  material,  it  is  necessary 
to  give  it  the  required  shape  before  it  is 
set  or  hardened  during  carbonization. 
This  is  accomplished  by  winding  the 
thread  on  a  suitable  block  or  form.  As 
in  the  case  of  the  bamboo  filament,  means 
must  be  provided  for  allowing  shrinkage 
to  take  place.  This  is  accomplished  by 
means  of  a  carbonizing  frame,  which  con- 
sists essentially  of  a  suitably  shaped  block 
and  an  end  piece  of  carbon,  connected  to- 


PREPARATION   OF  THE   FILAMENT.         95 

gether  by  sticks  of  wood.  These  sticks 
are  firmly  fixed  to  the  end  piece  and 
pass  loosely  into  openings  in  the  main 
block  which  rests  on  them.  The  threads 
to  be  carbonized,  are  wrapped  tightly 
around  the  block  and  end  piece,  which 
is  so  placed  in  the  carbonizing  box  that 
on  the  shrinkage  of  the  thread,  the 
wooden  sticks,  whose  dimensions  have 
been  carefully  selected,  shrink  to  the  same 
extent,  thus  permitting  the  upper  block  to 
slowly  descend  on  to  the  end  piece.  A 
number  of  such  frames  are  packed  to- 
gether in  a  carbon  box,  which  is  itself 
placed  in  a  crucible.  The  space  between 
box  and  crucible  is  filled  with  powdered 
carbon. 

In  the  carbonization  of  amyloid  threads, 
it  has  been  found  that  in  order  to  obtain 
the  best  results,  the  heat  must  be  very 


96      ELECTRIC   INCANDESCENT  LIGHTING. 

gradually  applied.  Should  the  crucibles 
be  exposed  to  a  sudden  increase  of  tem- 
perature, the  filament  contracting  too 
suddenly,  may  be  broken.  Moreover,  the 
gases  produced  by  distillation  might  possi- 
bly deposit  sufficient  carbon  on  the  sides 
of  the  filaments,  to  interfere  with  their 
homogeneity  and  also  to  cause  them  to 
cohere.  Consequently,  a  pyrometer  is  fre- 
quently used  in  connection  with  the 
furnace  in  order  to  regulate  its  tem- 
perature. The  time  required  to  effect  the 
carbonization  will  vary  with  the  size  and 
character  of  the  filaments.  Ordinary 
thread  filameuts  may  require  eighteen 
hours  for  their  proper  carbonization,  al- 
though a  longer  time  may  be  employed. 
The  period  required  for  carbonization, 
necessarily  varies  with  the  size  of  the  fila- 
ments, their  character  and  the  nature  of 
the  furnace. 


PREPARATION   OF  THE   FILAMENT.         97 

Incandescent  lamp  filaments  are  now 
sometimes  manufactured  by  a  squirting 
process.  This  is  in  the  main  a  secret 
process,  but  it  consists  essentially  in  ob- 
taining an  exceedingly  intimate  mixture 
of  carbonaceous  materials,  forming  them 
into  a  plastic  mass  and  subjecting  the 
same,  while  in  the  plastic  condition,  to 
powerful  pressure,  whereby  they  are  forced 
or  squirted  through  molds  in  die  plates. 
Means  are  devised  for  preserving  the  shape 
which  it  is  desired  that  this  material 
should  take,  and  then,  after  carefully  dry- 
ing the  same,  it  is  submitted  to  a  suitable 
carbonizing  process.  Experience  has  shown 
that  squirted  filaments  are  capable  of  being 
rendered  perfectly  uniform.  In  all  cases 
after  the  filaments  have  received  the  proper 
carbonization,  it  is  necessary  to  wait  until 
the  furnace  and  its  contents  are  cooled, 
before  removing  them  from  the  carboniz- 


98      ELECTRIC   INCANDESCENT  LIGHTING. 

ing  boxes,  both  on  account  of  their  fragile 
character,  and  for  the  sake  of  the  furnace, 
which  is  apt  to  be  injured  by  the  sudden 
chilling. 


CHAPTER  VI. 

MOUNTING    AND     TREATMENT     OF     FILAMENTS. 

HAVING  traced  the  filaments  up  to  the 
completion  of  their  carbonization,  we  will 
assume  that  they  are  ready  to  be  removed 
from  the  carbonizing  box.  As  already 
stated,  the  box  and  its  contents  are  sup- 
posed to  have  cooled  down  to  the  tem- 
perature of  the  room.  Care  must  be  exer- 
cised in  removing  the  filaments  from  the 
box,  since  the  carbonization  has  changed 
the  physical  nature  of  the  material,  and  the 
carbons  are  now  brittle,  though  hard  and 
elastic.  • 

The  next  step  in  the  manufacture  of  the 
lamp  now  begins  viz.,  the  mounting  of 


00 


100      ELECTRIC    INCANDESCENT   LIGHTING. 

the  filament,  or  placing  it  upon  a  glass  sup- 
port through  which  the  leading-in  wires, 
or  the  conductors  which  carry  the  current 
to  the  filament  are  sealed.  The  ends  of 
the  filament  are  attached  to  the  extremi- 
ties of  the  leading-iu  wires  by  any  suitable 
means.  Much  ingenuity  has  been  dis- 
played in  obtaining  a  suitable  mounting 
for  the  filament,  and  for  a  long  time  this 
mounting  constituted  the  weak-  point  in 
the  lamp.  Any  collection  of  incandescent 
lamps,  embracing  specimens  from  an  early 
period  in  the  history  of  the  art,  would  show 
how  marked  the  evolution  has  been  in  this 
particular. 

In  order  to  obtain  an  idea  of  the  rela- 
tion of  the  various  parts  of  «the  mounted 
filaments  reference  may  be  had  to  Fig.  12, 
which  shows  one  of  the  common  forms  of 
mounting.  A  glass  tube  T,  has  a  shoul- 


TREATMENT   OF   FILAMENTS. 


101 


der  blown  on  it  at  8.  Two  copper  wires 
MI,  w2)  ordinarily  0.015"  in  diameter,  are 
welded  to  short  pieces  of  platinum  wire, 


\  wt 
FIG.  12. — THE  MOUNTED  FILAMENT. 

the  method  generally  adopted  being  to 
hold  the  end  of  the  copper  wire  against 
the  end  of  the  platinum  wire  in  a  flame, 
when  they  fuse  together.  These  two 


102      ELECTRIC   INCANDESCENT   LIGHTING. 

wires  constitute  the  leading-in  wires. 
These  wires  are  then  laid  in  the  glass 
tube  T,  and  the  glass  is  fused  around  the 
platinum  wires  in  a  flat  seal  at  the  point 
/SJ  so  that  short  projections  of  the  plati- 
num p,  p,  extend  through  the  glass  seal. 
The  glass  seal  is  then  carefully  annealed. 
The  filament  f,  is  now  connected  with  its 
ends  to  the  wires  p,  p. 

When  it  is  remembered  that  the  opera- 
tion of  an  electric  lamp  necessarily  brings 
the  filament  to  a  white  heat,  it  will  be  evi- 
dent that  means  must  be  provided  either 
for  preventing  the  joints  at  p,  p,  from 
attaining  a  high  temperature ;  or,  if  such 
temperature  be  attained,  that  the  character 
of  the  joint  must  be  such  that  it  will  not 
suffer.  In  any  event  it  is  clear  that  the 
seal  S9  must  not  be  exposed  to  an  incan- 
descent temperature,  and,  therefore,  the 


TREATMENT   OF  FILAMENTS.  103 

platinum  extremities  p,  p,  must  remain 
comparatively  cool.  The  method  which 
is  always  adopted  is  to  provide  such  a 
cross  section  at  the  joints  p,  p,  that,  taken 
in  connection  with  the  thermal  conductiv- 
ity of  the  platinum  wires,  the  tempera- 
ture of  the  joints  will  be  much  below  the 
incandescing  temperature  of  the  rest  of  the 
filament.  In  the  earlier  forms  of  lamps, 
in  which  very  large  currents  were  usually 
employed,  this  result  was  accomplished  by 
providing  massive  terminals  connected 
with  the  carbon  filament,  possessing  so 
great  a  radiating  surface  that  their  tem- 
perature was  necessarily,  comparatively 
low.  Moreover,  since  most  of  these  early 
forms  of  lamps  did  not  employ  a  solid 
glass  seal,  it  was  still  further  necessary 
to  reduce  the  temperature  of  the  leading- 
in  wires  at  the  points  of  entry  by  means 
of  cement. 


104      ELECTRIC   INCANDESCENT   LIGHTING. 

Platinum   is  employed  where  the  glass 
is  fused   around   the  leading-IB   wires,  for 


FIG.  13.— HORSESHOE  LAMP. 


the   reason   that   the   expansion   and  con- 
traction of  platinum  is   almost   the   same 


TREATMENT   OF   FILAMENTS.  105 

as  that  of  glass.  The  expansion  of  glass 
rods  varies  from  0.0007  to  0.001  per  cent, 
of  their  length,  for  each  degree  Centigrade, 
or  just  about  the  mean  value  of  the 
expansion  of  platinum  wires.  When, 
therefore,  glass  is  sealed  around  a  plat- 
inum wire,  and  the  seal  is  heated,  the 
glass  and  the  platinum  expand  together, 
and,  on  cooling  contract  together.  If 
this  were  not  the  case,  there  would  be 
a  continual  tendency  to  shear  the  glass 
over  the  platinum  surface,  and  break 
the  seal  both  on  expansion  and  con- 
traction. Among  ordinary  metals  iron 
comes  next  to  platinum  as  regards  its 
expansion,  and  iron  has  been  employed  to 
some  extent  for  the  seal  in  incandescent 
lamps. 

Fig.    13,   represents   an    early   form   of 
lamp  in  which  this  method  of  connection 


106      ELECTRIC    INCANDESCENT   LIGHTING. 

was  employed.  A  filament  is  connected 
to  large  terminals  of  copper  supported  on 
an  insulating  bridge.  These  terminals  are 
further  connected  with  long  zig-zag  strips 
of  copper,  extending  to  the  base  of  the 
lamp,  for  the  purpose  of  ensuring  a  low 
temperature  where  they  pass  through  the 
base. 

In  some  of  the  earlier  lamps  of  the 
modern  type  the  ends  of  the  filaments 
were  made  of  enlarged  cross  section,  so  that 
they  were  not  only  more  readily  secured 
to  the  platinum  leading-in  wires,  but  also 
by  their  increased  mass  prevented  the  cur- 
rent from  raising  it  to  the  temperature  of 
incandescence.  In  Fig.  14,  a  filament  of 
bamboo  is  provided  with  enlarged  ends. 
In  some  cases  the  carbon  filaments,  after 
they  had  been  subjected  to  the  carboniz- 
ing process,  and  while  still  in  place  in 


TREATMENT   OF   FILAMENTS.  107 

the  carbonizing  box,  had  their  ends  thick- 
ened by  deposits  of  carbon,  produced  from 


FIG.  14.— BAMBOO  FILAMENT. 


108      ELECTRIC    INCANDESCENT   LIGHTING. 

the  decomposition  of  a-  carbonizable  gas, 
forced  into  the  mold  at  a  certain  stage 
in  the  process. 

A  very  early  form  of  joint  consisted  of 
a  platinum  bolt  and  nut,  as  shown  in 
Fig.  13.  A  small  screw  lamp  was  some- 
times employed  for  the  same  purpose  as 
shown  in  Fig.  15.  At  one  time,  small 
metal  blocks,  O,  C,  were  employed 
fastened  upon  the  enlarged  extremities  of 
the  filament,  as  shown  in  Fig.  16.  Some- 
times a  small  socket  was  formed  in  the 
end  of  the  wire,  and  the  carbon  was 
placed  in  this  receptacle  and  the  socket 
pressed  around  it.  In  another  form,  the 
socket  joint  was  secured  more  firmly  to 
the  carbon  by  covering  it  with  an  elec- 
trolytic coating  of  carbon,  or  the  wire  was 
wrapped  around  the  carbon  and  subse- 
quently secured  to  it  in  the  same  manner. 


TREATMENT   OF   FILAMENTS.  109 


FIG.  15. — EARLY  FORM  OP  JOINT  LAMP. 


110      ELECTRIC   INCANDESCENT   LIGHTING. 

This   proved   an   excellent   form  of  joint, 
and  was  employed  extensively  for  a  num- 


FIQ.  16.— EARLY  FORM  OF  CLAMP. 


TREATMENT   OF  I  fc^  AMENTA 'PL  fil^Y    £,  f 

ber  of  years.  It  has,  n^^er,  been  re- 
placed by  a  still  simpler  r^gcln^wbich  ' 
no  socket  is  employed,  but  one  en3ToT"t1ie 
filament  is  abutted  against  the  end  of  the 
platinum  wire,  and  carbon  is  deposited 
around  the  joint.  This  joint  is  obtained 
by  dipping  the  abutting  end  into  a  suit- 
able carbonizable  liquid  and  sending  a 
powerful  current  through  the  abutment 
wThile  in  the  liquid.  Under  these  con- 
ditions, a  decomposition  of  the  liquid 
occurs  and  hard  carbon  is  deposited 
on  the  joint,  thus  effecting  a  thorough 
seal.  At  the  present  time  the  still  simpler 
method  is  usually  adopted  of  cementing 
the  two  together  by  a  lump  of  carbon 
paste  or  dough. 

In  the  early  history  of  the  modern  in- 
candescent lamp,  the  filaments,  produced 
by  substantially  the  processes  already  de- 


112      ELECTRIC   INCANDESCENT   LIGHTING. 

scribed,  when  placed  in  the  exhausted 
lamp  chamber  and  rendered  incandescent 
by  the  passage  of  a  current  through  them, 
were  frequently  found  to  glow  irregularly, 
that  is  to  say,  there  were  parts  wThich  were 
rendered  vividly  incandescent  while  other 
parts  were  only  dull  red.  This  was  due 
to  the  fact  that  the  process  did  not  pro- 
duce homogeneous  carbon  filaments.  In 
other  words,  either  the  diameter  varied  at 
different  parts,  or  the  resistivity  of  the 
material  varied,  or  both.  Consequently, 
when  the  incandescing  current  was  sent 
through  the  filament,  and  the  temperature 
gradually  increased,  the  high  resistance 
parts  of  the  filament  first  began  to  glow, 
while  the  others  remained  comparatively 
cool,  the  heat  being  developed  by  the  cur- 
rent in  proportion  to  the  resistance  en- 
countered. If  such  a  spotted  filament 
were  employed  in  the  lamp  and  the  tern- 


TREATMENT  OF  FILAMENTS.     113 

perature  raised  by  increasing  the  cur- 
rent, so  as  to  make  all  parts  of  the  fila- 
ment glow,  then  the  temperature  of  the 
high  resistance  portions  would  probably 
be  raised  beyond  the  limit  of  safety 
and  the  life  of  the  lamp  would  conse- 
quently be  much  shortened ;  while,  on  the 
contrary,  if  the  higher  resistance  portions 
of  the  filament  wrere  limited  to  the  safe 
temperature,  the  lower  resistance  portions 
would  be  at  so  low  a  temperature,  that  the 
candle-power  of  the  entire  lamp  would  be 
unduly  low. 

This  difficulty  was  happily  overcome  by 
an  exceedingly  ingenious  process,  gener- 
ally called  the  flashing  process,  which 
consisted  essentially  in  a  means  whereby 
carbon  was  caused  to  be  deposited  only 
upon  those  portions  of  the  filaments  whose 
resistance  was  higher  than  the  rest.  In 


114      ELECTRIC    INCANDESCENT   LIGHTING. 

other  words,  if  the  filament  were  unduly 
narrow  at  some  particular  spot,  or  had  an 
undue  resistivity  at  such  spot,  then  carbon 
would  be  deposited  upon  this  spot  only. 

The  flashing  process  is  carried  on  sub- 
stantially as  follows.  The  mounted  fila- 
ment is  placed  in  a  suitable  chamber  from 
which  the  air  has  been  removed,  and 
which  is  subsequently  filled  with  a  hydro- 
carbon vapor.  An  electric  current,  whose 
strength  is  gradually  increased,  is  then 
sent  through  the  filament.  A  hydro- 
carbon gas  or  vapor,  suffers  decomposition 
in  the  presence  of  a  heated  surface  as  soon 
as  a  certain  temperature  is  reached.  As 
the  current  gradually  increases,  the  carbon 
filament  begins  to  glow  at  its  point  of 
greatest  resistance,  and  this  point,  conse- 
quently, receives  a  deposit  of  carbon,  thus 
decreasing  the  resistance  locally.  If  this 


TREATMENT   OF   FILAMENTS.  115 

current  strength  were  maintained,  the  car- 
bon would  cease  to  glow  at  these  points. 
If,  however,  the  current  strength  be  fur- 
ther increased,  the  carbon  would  begin  to 
glow  at  the  point  of  next  highest  resist- 
ance, and  this  in  turn,  receiving  a  deposit, 
would  cease  to  glow  at  this  current 
strength.  It  will  be  readily  seen,  there- 
fore, that  as  the  current  strength  is  gradu- 
ally increased,  the  filament  receives  a 
deposit  at  those  portions  of  its  mass  only 
where  it  needs  increase  in  conducting 
power,  and  soon  the  entire  filament  will 
glow  with  a  uniform  intensity  of  light. 

It  must  not  be  supposed,  that  the  car- 
bon is  now  absolutely  of  the  same  area 
of  cross  section,  or  of  the  same  thickness 
throughout.  The  flashing  process  has 
rendered  it  electrically,  but  not  mechani- 
cally, homogeneous.  We  have  correctly 


116      ELECTRIC    INCANDESCENT   LIGHTING. 

described  the  process  as  consisting  of  suc- 
cessive steps  reached  by  gradually  increas- 
ing the  current  strength.  In  point  of  fact, 
these  steps  follow  one  another  so  rapidly 
that  the  process  at  first  sight  may  seem 
to  be  almost  instantaneous,  only  a  few 
seconds  being  required  for  an  exceedingly 
spotted  carbon  to  emit  a  uniform  glow. 

Although  at  the  present  day  improve- 
ments in  manufacture  have  resulted  in  the 
production  of  filaments,  which  are  so 
nearly  uniform  in  their  resistance  that 
they  will  glow  uniformly  when  placed  in 
the  lamp,  and,  therefore,  do  not  require 
to  be  subjected  to  the  flashing  process, 
nevertheless,  since  this  process  results  in 
giving  to  the  filament  other  valuable  prop- 
erties, it  is  still  generally  practiced.  Not 
only  are  the  surfaces  of  flashed  carbon 
filaments  harder  than  those  which  have  not 


TREATMENT  OF   FILAMENTS.  117 

undergone  tins  process,  but  the  amount  of 
liglit  which  they  emit  for  a  given  current 
strength  is  markedly  increased. 

The  flashing  process  is  sometimes 
carried  on  in  liquids,  such  as  beuzine,  the 
filaments  being  dipped  in  the  liquid  and 
the  current,  as  before,  supplied  in  gradu- 
ally increasing  strength.  In  such  cases, 
however,  the  decomposition  of  the  liquid 
produces  an  atmosphere  of  gas  around 
the  filament  so  that  the  difference  in  the 
process  is  rather  in  appearance  than  in 
reality. 


CHAPTER  VII. 

SEALING-IN   AND    EXHAUSTION. 

THE  mounted  and  flashed  filament  has 
now  to  be  inserted  in  an  enclosing  glass 
chamber,  in  which  it  is  hermetically  sealed. 
This  sealing- in,  is  preferably  accomplished 
by  the  actual  fusion  of  the  glass  stem  to 
the  lower  part  of  the  globe.  It  will  be 
interesting,  therefore,  to  examine  in  detail 
the  method  generally  employed  in  the 
manufacture  of  the  incandescent  lamp 
chamber  and  its  hermetical  closure  on 
sealing-in. 

Fig.  17,  represents  the  successive  steps 
that  are  generally  taken  in  the  sealing-in 

118 


SEALING-IN   AND   EXHAUSTION. 


119 


of    the    mounted   filament    in    the    lamp 
chamber.     The    glass    lamp   chamber  A, 


FIG.  17.— STEPS  OP  SEALING-IN  PROCESS. 

has  the  form  shown,  the  open  tubular  pro- 
jection being  left  at  £,  for  the  exhaustion 
of  the  chamber.  The  open  end  of  the 


120      ELECTRIC    INCANDESCENT   LIGHTING. 

chamber  A,  is  of  such  dimensions  that  the 
mounted  filament  can  be  introduced  into 
it  up  to  the  shoulder  d,  which  then  rests 
in  contact  with  the  lower  end  a,  of  the 
chamber.  The  stem  is  then  grasped  by 
the  glass-blower  in  one  hand,  and  the 
tubular  end  of  the  chamber  in  the  other, 
and  the  two  revolved  together  as  one 
piece,  in  a  suitable  blow-pipe  flame  di- 
rected upon  the  shoulder  or  joint,  until 
the  fusing  temperature  is  reached,  and  the 
edge  a,  becomes  hermetically  sealed  with 
the  shoulder  d.  By  this  means  it  will  be 
seen  that  an  enclosing  chamber,  made  en- 
tirely of  glass,  is  provided  with  leading-in 
wires  passing  through  the  support  at  />,  p. 
In  the  early  history  of  the  art,  it  was 
necessary  that  this  delicate  operation 
should  be  performed  by  a  skilled  glass- 
blower,  but  during  recent  years,  machines 
have  been  introduced  which  grasp  the 


SEALING-IN    AND    EXHAUSTION. 

globe  aud  stein  and  revolve  them  in  the 
blow-pipe  flame  with  the  requisite  amount 
of  pressure.  The  machine  seal,  so  ef- 
fected, is  made  as  swiftly  and  neatly  as 
that  of  the  most  expert  workman.  The 
sealed-in  lamp  is  then  carefully  annealed, 
by  subjecting  it  to  the  action  of  a  gradu- 
ally diminished  heat,  while  under  the 
action  of  a  roller.  Great  care  is  neces- 
sary that  the  annealing  of  the  joint  should 
be  thoroughly  effected. 

Attempts  have  been  made,  at  different 
times,  to  produce  a  lamp  in  which  a  'me- 
chanical seal  was  effected  between  the 
stem  and  the  globe,  instead  of  a  seal  by 
fusion.  Such  a  seal  possesses  the  advant- 
age of  permitting  the  lamp  to  be  readily 
repaired  on  the  breaking  of  the  filament. 
Figs.  18,  19,  and  20,  show  a  form  of  Kich 
stopper-lamp,  as  it  is  generally  called. 


122      ELECTRIC   INCANDESCENT   LIGHTING. 


Fig.  18,  represents  the  mounted  filament, 
which  is  connected  to  the  extremities  of 
two  iron  wires  sealed  into  the  neck  or 


FIG.  18. — STOPPER-MOUNTED  FILAMENT  OF  INCAN- 
DESCENT LAMP. 

stem  L.  We  have  already  pointed  out 
that  iron  is  sometimes  employed  for  this 
purpose.  The  stopper  portion  of  the  stem 


SEALING-IN   AND   EXHAUSTION.          123 

at  /SJ  is  ground  by  machinery  to  fit  a  simi- 
larly ground  seat  in  the  opening  of  the 
lamp  globe,  which  is  shown  at  A,  Fig.  19. 
The  mounted  filament  is  inserted  into  the 
lamp  chamber,  and  the  stopper  secured  in 
its  seat  by  a  flexible  cement.  A  brass 
shell  is  then  secured  around  the  base  B  of 
the  lamp,  enabling  connections  to  be  main- 
tained with  its  terminals,  as  shown  in 
Fig.  20. 

The  mounted  filament,  having  thus  been 
introduced  into  the  lamp  chamber,  and  the 
base  of  the  lamp  hermetically  sealed,  the 
next  step  is  the  exhaustion  of  the  lamp 
chamber.  An  exceedingly  small  quantity 
of  air  left  in  the  chamber  will  contain 
sufficient  oxygen  to  cause  rapid  destruction 
of  the  lamp  filament.  Consequently,  it  is 
necessary  to  remove,  as  far  as  possible,  all 
traces  of  air  from  the  interior.  This  is 


124      ELECTRIC   INCANDESCENT   LIGHTING, 


FIG.  19.— GLOBE  OF  STOPPER  LAMP. 


SEALING-IN   AND    EXHAUSTION.          125 

accomplished  by  means  of  pumps.  The 
ordinary  mechanical  air-pump,  of  the  auto- 
matic valve  type ;  i.  e.,  in  which  the 
valves  are  opened  and  closed  automatically 
by  the  motion  of  the  piston,  is  capable 
of  producing  fairly  high  vacua,  but  not 
sufficiently  high  for  the  purposes  of  being 
used  alone  in  the  exhaustion  of  the  lamps, 
since  the  residual  air  would  still  be  detri- 
mental. Mechanical  pumps,  however,  are 
often  used  for  producing  a  rapid  exhaus- 
tion of  the  lamp  chamber,  the  final  exhaus- 
tion being  accomplished  by  means  of  a 
mercury  pump.  The  operation  of  the  mer- 
cury pump,  however,  is  so  simple  in  practice 
and  efficient  in  action,  that  in  some  cases,  the 
use  of  the  mechanical  pump  is  dispensed 
with,  and  the  entire  process  of  exhaustion 
is  carried  on  by  the  mercury  pump  alone. 

A  great  variety  of  mercury  pumps  have 


126      ELECTRIC   INCANDESCENT  LIGHTING. 


FIG.  20.— COMPLETED  STOPPER  LAMP. 


PROPERTY 

SEALING-IN   ANJ^xJ^QIAUSTION.         127 


been  devised,  all  of 
niently  divided  into  two  classes"?1 
those  of  the  Geissler  type,  in  which  the 
vacuum  is  obtained  by  utilizing  the  prin- 
ciple of  the  so-called  Torricellian  vacuum, 
of  the  barometer  tube,  and  those  of  the 
Sprengel  type,  in  which  the  vacuum  is 
obtained  by  the  fall  of  a  stream  of  mer- 
cury. When  a  column  of  mercury  is  per- 
mitted to  fall  through  a  vertical  tube, 
connected  near  its  upper  end  by  a  branch 
tube  with  the  chamber  to  be  exhausted, 
the  air  will  be  carried  away  from  the 
chamber  by  becoming  entangled  as  bub- 
bles in  the  falling  column.  Mercury 
pumps  of  this  character  are  well  adapted 
to  the  exhaustion  of  lamps,  owing  to  the 
simplicity  and  efficiency  of  their  action. 

When  the  proper  degree  of  vacuum  is 
obtained,  the  lamp  is  sealed-off  by  fusing 


128      ELECTRIC   INCANDESCENT   LIGHTING. 

the  tube  at  tlie  top  of  the  lamp  chamber, 
with  a  blow-pipe  flame,  a  constriction  being 
provided  in  the  tubulure  I,  at  &1  as  shown 
in  Fig.  17,  for  facilitating  this  process. 
In  the  early  state  of  the  art  this  sealing-off 
was  effected  while  both  the  lamp  and  the 
filament  were  cold.  It  was  found,  when 
thus  sealed-off,  that,  although  the  proper 
vacuum  had  been  obtained,  and  the  lamp 
operated  satisfactorily  for  a  while,  yet  the 
vacuum  soon  invariably  deteriorated,  so 
that  the  life  of  the  lamp  was  unduly  short- 
ened. The  explanation  was  at  last  found 
in  the  fact  that  gases  were  occluded  or 
absorbed  in  the  carbon  filament,  as  well  as 
condensed  on  the  inner  surface  of  the  globe. 
These  gases  adhered  to  the  filament,  or  to 
the  globe,  with  too  great  a  force  to  per- 
mit them  to  escape  into  the  lamp  chamber 
during  the  process  of  exhaustion.  When, 
however,  the  lamp  was  lighted  after  con- 


SEALING-IN   AND   EXHAUSTION.          129 

eluding  the  process  of  exhaustion,  the  in- 
tense heat  of  the  filament  disengaged 
these  gases  which  reduced  the  vacuum  in- 
juriously. The  remedy  is  simple.  As 
soon  as  a  fairly  good  vacuum  is  obtained 
in  the  lamp,  an  electric  current  is  sent 
through  the  filament  and  the  last  stages  of 
the  pumping  process  are  carried  on  while 
the  filament  is  aglow.  Immediately  be- 
fore sealing-off,  the  current  is  increased 
beyond  the  strength  intended  to  be  em- 
ployed in  practice,  and  the  lamps  sealed 
while  the  pumping  is  carried  on.  By  this 
means  the  occluded  gases  in  the  filament 
and  on  the  globe  are  carried  off,  and  this 
process  has  done  much  to  improve  the  lamp. 

When  incandescent  lamps  were  first 
manufactured  on  a  large  scale,  an  effort 
was  made  to  obtain  as  high  a.  vacuum  as 
possible,  and  pumps  were  employed  which, 


130      ELECTRIC   INCANDESCENT  LIGHTING. 

it  was  claimed,  left  a  residual  atmosphere 
in  the  lamp  chamber  of  but  1,000,000th  of 
its  original  amount;  that  is  that  999,999 
parts  of  air  out  of  every  million  had  been 
removed.  Even  at  the  present  time,  while 
it  is  generally  considered  that  residual 
atmospheres  of  air,  containing  as  they 
necessarily  must  traces  of  oxygen,  result  in 
a  decreased  life  of  the  lamp,  yet  it  may  be 
asserted,  as  a  result  of  actual  experience, 
that  residual  atmospheres  of  certain  gases, 
such  as  chlorine  or  bromine,  or  mixtures 
of  the  same,  may  not  only  be  innocuous 
but  actually  advantageous. 

It  is  quite  possible,  during  the  opera- 
tion of  a  lamp,  the  sealing-off  of  which 
has  been  thoroughly  made,  that  the  vacuum 
may  actually  improve  rather  than  dete- 
riorate ;  for,  in  the  disintegration  of  the 
carbon,  to  which  we  shall  allude  in  a  sub- 


SEALING-IN   AND   EXHAUSTION.          131 

sequent  chapter,  a  deposit  of  finely  divided 
carbon  takes  place  inside  the  lamp  cham- 
ber. This  carbon  possessing,  as  it  does, 
the  power  of  occluding  or  absorbing  resid- 
ual atmospheres,  would  naturally  tend  to 
improve  the  vacuum  during  use. 

The  exhausted  and  sealed  lamp  must 
now  be  provided  with  a  base,  whereby  it 
can  be  readily  placed  in  a  socket  or  sup- 
port. The  lamp  base  is  so  arranged  that 
two  metallic  portions,  suitably  insulated 
from  one  another,  are  connected  to  the 
ends  of  the  leading-in  wires.  These  por- 
tions on  the  base  are  adapted  to  connect 
the  lamp  with  the  circuit  wires  by  the 
mere  act  of  placing  it  in  the  lamp  socket. 
Various  forms  of  lamp  bases  are  employed 
as  we  shall  see  hereafter.  The  lamp  base 
is  attached  to  the  lamp  by  a  cement,  gen- 
erally of  plaster  of  Paris. 


132      ELECTRIC   INCANDESCENT  LIGHTING-. 

Some  of  the  more  usual  forms  of  lamp 
bases  are  shown  in  Fig.  21  at  A,  B,  C 
and  D.  The  two  separate  metallic  pieces, 
which  are  electrically  connected  to  the 
ends  of  the  leading-in  wires,  are,  in  all 


FIG.  21.— LAMP  BASES. 

cases,  indicated  by  the  letters  a  and  Z>. 
An  inspection  of  the  figure  will  show  that 
A^  has  a  central  contact  pin  as  one  termi- 
nal, and  a  concentric  brass  ring  as  the 
other  terminal.  B,  has  a  central  pin  as 
one  terminal,  and  an  external  concentric 
cylinder  as  the  other.  At  (7,  two  concen- 
tric cylinders  are  employed,  the  inner  one 
has,  however,  a  screw  thread  for  securing 
it  in  its  socket.  D,  has  a  screw  shell  as 


SEALING-IN   AND   EXHAUSTION.          133 

one   terminal,   and   a   central   cap   as  the 
other  terminal. 


It  is  sometimes  convenient  to  fit  a  lamp 
of    one    manufacture    into    a    socket    of 


FIG.  22. — LAMP  ADAPTERS. 


another  manufacture.  For  this  purpose  a 
device  called  a  lamp  adapter  is  employed. 
An  adapter  consists  essentially  of  an  exte- 
rior base  and  an  interior  connection  piece. 


134      ELECTRIC   INCANDESCENT    LIGHTING. 

In  Fig.  22,  four  adapters  are  shown  suit- 
able for  attachment  to  a  stopper  lamp,  and 
provided  with  bases  corresponding  to  the 
lamp  bases  shown  in  A,  B,  C\  D,  of  Fig. 
21,  similar  letters  corresponding  in  the 
two  figures.  The  use  of  stopper  lamps  has, 
however,  been  abandoned. 


CHAPTER  VIII. 

LAMP    FITTINGS. 

the  removal  of  the  lamp  from  the 
pumps,  it  is  tested  for  candle-power,  and 
marked  in  volts  for  the  pressure  which 
should  be  supplied  to  it  in  operation. 

Some  examples  of  finished  lamps  are 
shown  in  Fig.  23.  These  lamps  are  all  of 
the  same  type  and  differ  only  in  the  form 
of  base.  The  bases  of  these  lamps  differ 
so  as  to  permit  each  lamp  to  be  used  on 
some  particular  socket. 

One  of  the  simplest  forms  of  sockets 
intended  for  inexpensive  work,  especially 


135 


136      ELECTRIC    INCANDESCENT   LIGHTING. 


FIG.  23. — COMPLETED  INCANDESCENT  LAMPS. 


LAMP    FITTINGS. 


137 


where  the  lamps  are  not  open  to  direct  ob- 
servation, such  as  at  the  foot  or  side  lights 
of  theatres,  is  shown  in  Fig.  24.  This 


FIG.  24. — SIMPLE  FORM  OP  SOCKET. 

socket  is  intended  to  receive  a  lamp  with  a 
screw  base.  A  wooden  shell  Z,  is  screwed 
to  the  wall  or  other  support,  by  ordinary 
screws  passing  through  the  screw  holes, 
one  of  which  is  seen  at  S.  A  and  ^?,  are 
brass  screws  intended  for  the  reception  of 


138      ELECTRIC    INCANDESCENT   LIGHTING. 

the  circuit  wires   or  mains,  and  are  con- 
nected respectively  to  the  brass  screw  shell 


FIG.  25. — KEYLESS  WALL-SOCKET. 

(7,  and  a  central  cap  beneath.     These  will 
make  contact  with  the  two  insulated  por- 


LAMP   FITTINGS.  139 

tions  of  the  base  of  the  lamp  when  the 
lamp  is  screwed  in. 


FIG.  26. — KEY  WALL-SOCKET. 

Fig.  25,  shows  a  more  sightly  form  of 
keyless  socket,  that  is,  a  socket  which  is  not 


140      ELECTKIC    INCANDESCENT   LIGHTING. 

provided  with  a  key  or  switch,  and  which, 
therefore,  constantly  maintains  connection 
between  the  mains  and  the  lamp.  The 
base  13  J?,  is  of  porcelain,  and  is  fixed  in 
position  by  screws  passing  through  screw 
holes  C\  C.  Supply  wires,  connected  with 
the  mains,  pass  beneath  through  the 
grooves  W,  W.  Connections  are  main- 
tained through  the  interior  of  the  shell. 

A  socket  of  a  similar  character,  but  pro- 
vided with  a  key  K,  is  shown  in  Fig.  26. 
In  this  case  the  lamp  is  lighted  or  extin- 
guished by  the  turning  of  the  key.  In 
the  case  of  keyless  sockets  the  lamps  are 
turned  on  or  off  by  the  action  of  a  distant 
switch. 

Socket  keys,  open  and  close  the  circuit  of 
a  lamp  at  one  point  in  a  variety  of  ways. 
Two  forms  of  socket  keys  are  shown  in 


LAMP   FITTINGS. 


141 


Figs.  27  and  28.  Fig.  27,  shows  a  socket 
suitable  for  use  with  a  lamp  base  of  type 
B,  Fig.  21;  and  Fig.  28,  shows  a  socket 
suitable  for  use  with  the  lamp  base  of  type 


PIG.  27.— DETAILS  OP  SOCKET. 

Oj  in  that  figure.  In  Fig.  27,  the  turning 
of  the  key  K,  makes  contact  between  the 
brass  segments  b,  Z>,  through  the  interme- 
diary of  the  cam,  on  the  extremity  of  the 
key  axis.  In  Fig.  28,  a  similar  method  is 


142      ELECTRIC   INCANDESCENT   LIGHTING. 

employed.  Here  the  movement  of  the 
key  closes  connection  between  contacts 
by  ^  through  the  metal  piece  C. 


FIG.  28. — DETAILS  OP  LAMP  SOCKET. 

Fig.  29,  represents  in  cross-section  a 
lamp  with  a  screw  base  in  its  socket. 
The  current  is  turned  on  or  off  at  the  key 
K.  6r,  is  the  globe,  and  T,  the  tip  at  which 
the  lamp  was  sealed  on  removal  from  the 
pump ;  Pj  is  the  filament ;  89  the  seal  of 
the  leading-in  wires ;  W,  the  welds  be- 
tween the  platinum  and  the  copper  lead- 


" 


JP 

FIG.  29.— LAMP  AND  SOCKET  SHOWING  CONNECTIONS. 


144      ELECTRIC   INCANDESCENT   LIGHTING. 

ing-in  wires;  $',  the  seal  of  the  lamp  stem 
with  the  glass  chamber.  Z,  Z,  are  projec- 
tions of  the  glass  on  the  surface  of  the 
shoulder,  intended  to  aid  in  securing  the 

/  o 

lamp  in  its  plaster  of  Paris  cement.  6Yand 
12,  are  the  cap  and  screw  metallic  pieces  of 
the  base,  each  in  soldered  connection  with 
one  leading-in  wire  as  shown.  A  and  J3, 
are  the  cap  and  screw  connections  of  the 
socket,  each  in  connection  with  one  of  the 
external  wires  entering  the  socket  through 
the  pipe  or  metallic  support  P.  One  of 
these  wires  is  connected  directly  with  the 
brass  shell  A,  while  the  other  is  connected 
with  the  cap  />,  only  through  the  interme- 
diary of  the  key  K.  M  M,  is  the  external 
brass  shell  of  the  socket,  insulated  from 
the  interior  portions  by  the  hard  rubber 
ring  n  n. 

When  an  incandescent  lamp  is  supported 


LAMP   FITTINGS. 


145 


by  a  flexible  cord,  it  usually  requires  both 
hands  to  turn  the  key  at  the  socket  on  or 
off,  one  to  hold  the  lamp,  and  the  other  to 


FIG.  30. — Pusn  BUTTON  KEY  SOCKET. 

turn  the  key.  Fig.  30,  shows  a  device  by 
which  the  turning  on  or  off  can  be  accom- 
plished by  the  hand  which  holds  the 


146      ELECTRIC   INCANDESCENT   LIGHTING. 

socket.  This  is  accomplished  in  replacing 
the  ordinary  key  by  two  pressure  buttons. 
Pressure  upon  the  stud  AJ  forces  it  home 
until  it  is  locked  by  the  trigger  B,  thus 


PIG.  31.— SPRING  SOCKET  FOR  SCREW  BASE. 

turning  on  the  lamp  and  keeping  it  turned 
on.  Pressure  on  the  trigger  B,  releases 
the  push  A.,  which  returns  to  its  original 
position  under  the  action  of  a  spring. 

Fig.  31,  shows  a  form  of  spring  socket  for 
a  screw  lamp  base.      For  temporary  work, 


LAMP   FITTINGS. 


147 


such  as  exhibitions,  etc.,  where  the  expense 
of  permanent  fixtures  would  not  be  justi- 
fied, a  temporary  socket  is  sometimes  em- 
ployed, as  shown  in  Fig.  32.  It  consists  of 


FIG.  32.— TEMPORARY  SOCKETS. 

a  spiral  spring  holding  the  screw  base  of 
the  lamp,  and  connected  with  one  supply 
wire  W,  while  the  brass  screw  in  the  centre 
of  the  spiral  is  connected  with  a  second 
supply  wire  beneath  the  wooden  base  bar 


148      ELECTRIC   INCANDESCENT   LIGHTING. 

Such  construction  is,  of  course,  not  re- 
garded as  safe  for  permanent  use  in 
buildings. 

Where  lamps    are    placed   in   positions 
exposed  to  the  weather,  it  is  necessary  to 


FIG.  33. — WEATHER-PROOF  SOCKETS. 

employ  some  form  of  weather-proof  socket. 
Two  forms  of  such  sockets  in  common  use 
are  shown  in  Fig.  33,  that  on  the  right  hand 
side  being  of  glass,  and  that  on  the  left, 


LAMP   FITTINGS.  149 

of  hard  rubber  or  composition.  These 
sockets  are  intended  for  the  reception  of 
screw  bases. 

Various  forms  of  reflecting  surfaces  are 
employed  in  connection  with  the  lamps  so 


FIG.  34.— METALLIC  SHADE  FOB  REFLECTING  LIGHT 
DOWNWARDS. 

as  to  throw  the  light  in  any  desired  direc- 
tion. Two  such  forms  of  lamp  shades, 
devised  to  throw  the  light  downwards, 


150      ELECTRIC   INCANDESCENT  LIGHTING. 

are  shown  in  Figs.  34  and  35.  The  depth 
of  the  shade  will  vary  with  the  character 
of  the  illumination  required.  That  shown 
in  Fig.  34,  is  suitable  for  the  illumination 
of  desks  from  above.  Fig.  35,  is  suitable 


FIG.  35. — METALLIC  SHADE  FOR  REFLECTING  LIGHT 
DOWNWARDS. 


for  the  illumination  of  a  billiard  table. 
Fig.  36,  shows  a  form  of  half  shade  some- 
times employed  for  desk  use.  Here  one 
half  of  the  lamp  only  is  covered  by  the 


LAMP   FITTINGS.  151 

shade  which  in  outline  conforms  with  the 
shape  of  the  lamp,  the  inside  of  the  shade 
being  provided  with  a  good  reflecting  sur- 
face to  throw  the  light  downwards. 


FIG.  36.— METAL  HALF  SHADE  FOR  DESK  USE. 

It  is  important  in  order  to  ensure 
good  illumination  for  reading,  that  all 
portions  of  the  printed  page  shall  be 
equally  lighted.  Although  this  is  gener- 


152      ELECTRIC    INCANDESCENT   LIGHTING. 

ally  secured  by  the  aid  of  aiiy  good  shade, 
yet  it  is  often  preferable  to  employ  for 
this  purpose  the  form  of  shade  and  en- 
closing globe  shown  in  Fig.  37. 


FIG.  37.— REFLECTOR  SHADE. 

i  Instead  of  forming  the  lamp  shade  out 
of  a  single  surface,  a  number  of  sur- 
faces are  sometimes  employed,  either  plane 
or  curved.  Figs.  38  and  39  represent 


LAMP   FITTINGS.  153 

panel  reflectors  j  i.  e.,  reflectors  composed  of 
strips  or  panels  of  silvered  glass.     These 


FIG.  38. — CONCAVE  PANEL  SHADE  AND  REFLECTOR. 

reflectors  are  suitable  for  store  windows  or 
railway  stations.  The  shade  in  Fig.  38, 
is  designed  to  throw  light  downwards  from 


FIG.  39.— CONCAVE  PANEL  SHADE  AND  REFLECTOR. 


154      ELECTRIC   INCANDESCENT   LIGHTING. 

its  concave  surface,  and  Fig.  39  to  throw 
the  light  outwards  from  its  convex  surface 
as  well  as  downwards.  Finally,  reflectors 
of  similar  forms  are  also  arranged  to  oper- 


FIG.  40. — PANEL  REFLECTOR  AND  SHADE  FOR  CLUSTER. 

ate  with  clusters  of  lights  to  illumine 
larger  halls.  A  concave  panel  reflector  of 
this  type  is  shown  in  Fig.  40. 

Sometimes  corrugated  silvered  glass  is 
employed  in  various  forms  for  reflecting 


LAMP   FITTINGS.  155 

purposes.     Fig   41,   shows   a   reflector   of 
this  type  made  in  the  form  of  a  shade. 


FIG.  41. — CORRUGATED  REFLECTOR  AND  SHADE. 

Even  transparent  or  translucent  sub- 
stances may  at  times  be  employed  for 
reflectors.  In  such  cases  they  aid  in 
scattering  light  downwards  as  well  as  in 


156      JflLKCTKIO   INCANDESCENT   LIGHTING. 

reflecting  it.  Materials  employed  for  this 
purpose  are  glass  and  porcelain,  either 
plain  or  corrugated,  transparent  or  trans- 


FIG.  42. — GLASS  SHADES. 

lucent.     Fig,  42,  shows  a  variety  of  shades 
employed  for  such  purposes. 

Owing  to  the  fragile  nature  of   the  in- 
candescent lamp  chamber,  it  is  necessary, 


LAMP   FITTINGS. 


157 


when  lamps  are  placed  in  exposed  posi- 
tions, to  protect  them  from  accidental 
destruction  by  blows.  For  this  purpose 
wire  gratings  or  shields  are  arranged,  of 


FIG.  43.— HALF  WIRE-GUARD. 

such  form  and  outline  as  shall  not  seriously 
interfere  with  the  light.  Such  grat- 
ings would,  of  course,  be  inadmissible  in 
any  situation  where  marked  shadows 


158      ELECTRIC   INCANDESCENT  LIGHTING. 

are  objectionable,  and  should,  therefore, 
only  be  employed  in  cellars,  underground 
passages,  or  in  similar  situations.  Fig.  43, 
shows  a  form  of  half  wire-guard,  which, 


FlG.    44.—  FCLL,   WlRE-GUAKD. 

as  its  name  indicates,  only  surrounds 
a  portion  of  the  lamp  proper.  Fig.  44, 
shows  a  full  wire-guard  surrounding  the 
entire  lamp.  In  Figs.  45  and  46,  some 


LAMP   FITTINGS.  159 

forms  of  wire-guards  are  shown,  suitable 

O  ' 

for   portable   or   hanging  lamps. 

Sometimes,  instead  of  employing  a  wire 
guard  to   protect   the  lamp,   the   lamp  is 


FIG.  45.— WiRE-GuAKDS  FOR  SUSPENDED  LAMPS. 

entirely  surrounded  by  an  air-tight  or 
a  steam-tight  glass  lamp  chamber  as  in 
Fig.  47.  This  globe  consists  of  two  parts, 
a  cylindrical  glass  cover  with  a  rounded 


160      ELECTRIC   INCANDESCENT   LIGHTING. 

end,  provided  with  a  screw  thread  metallic 
cap,  capable  of  tightly  fitting  into  the  base 


FIG.  46. — PORTABLE  LAMP  GUARD. 

as  shown.  A  steam-tight  lamp  chamber  is 
employed  under  circumstances  where  it  is 
either  desired  to  protect  the  lamp  from  cor- 


LAMP   FITTINGS. 


161 


FIG.  47. — STEAM-TIGHT  LAMP  CHAMBER. 

rosive  vapors,  from  spray  at  sea,  or  for  the 
purpose  of  avoiding  any  possible  accident 
which  might  result,  from  the  explosion  of 


162      ELECTRIC   INCANDESCENT  LIGHTING. 

inflammable  gases  or  clouds  of  dust,  on  the 
accidental  breaking  of  the  lamp  chamber 
and  globe.  It  will,  of  course,  be  under- 
stood that  the  use  of  any  form  of  wire 
grating,  or  steam-tight  globe,  must  neces- 
sarily be  attended  by  a  marked  decrease  in 
the  useful  illumination  of  the  lamp. 


CHAPTER  IX. 

THE    INCANDESCING    LAMP. 

WE  have  now  traced  the  manufacture  of 
the  lamp  up  to  the  time  when  it  is  ready 
to  be  connected  with  the  supply  wires  and 
actuated  by  the  electric  current.  With  this 
the  manufacture  of  the  incandescent  lamp, 
that  is  a  lamp  capable  of  being  rendered 
incandescent,  now  ceases,  and  the  story  of 
the  incandescing  lamp,  and  the  theory  of 
its  operation  begins.  We  will,  therefore, 
trace  in  this  chapter  such  theoretical  con- 
siderations as  enter  into  the  action  of  the 
incandescing  lamp. 

An  incandescing  lamp  may  be  regarded 
as  an  electro-receptive  device,  wherein  the 


164      ELECTRIC    INCANDESCENT   LIGHTING. 

energy  of  the  electric  current  is  being  con- 
verted into  heat  energy,  part  of  which 
is  luminous.  It  is,  therefore,  necessary, 
at  the  outset,  to  determine  the  amount 
of  energy  which  the  lamp  is  absorb- 
ing. This,  as  we  have  already  seen,  is 
equal  to  the  product  of  the  number  of  am- 
peres, or  the  current  strength  supplied  to 
the  lamp,  and  the  pressure  in  volts  at  the 
lamp  terminals.  If  the  resistance  of  a 
lamp,  when  hot,  is  200  ohms,  and  the  pres- 
sure between  the  mains  100  volts,  then  the 
current  which  will  pass  through  the  lamp 

will  be  -    -  —  1/2  ampere,  and  the  activity 
200 

supplied  will  be  1/2  X  100  =  50  watts  or 
h  horse-power. 


The    temperature   which  an  activity  of 
50    watts,    will  .produce   in    a   lamp   fila- 


THE   INCANDESCING   LAMP.  165 

merit,  depends  both  upon  the  extent 
of  the  surface  area  of  the  filament  and 
upon  the  character  of  its  surface.  If 
the  surface  of  the  filament  be  large,  the 
activity  per  square  inch,  or  per  square  cen- 
timetre, will  be  comparatively  small,  and 
the  filament  will  not  be  highly  heated.  If, 
on  the  other  hand,  the  surface  area  of  the 
filament  be  small,  the  intensity  of  its  sur- 
face activity  will  be  great,  and  the  tem- 
perature of  the  filament  will  be  high. 
The  surface  activity  of  an  incandescing 
filament  is,  approximately,  from  70  to  100 

watts  per  square  centimetre,  or  450  to  650 

/» 

watts  per  square  inch ;  i.  e.,  about  T7)^ns 

o 

to  T^ths  of  a  horse-power  per  square  inch 
of  surface. 

The  electric  arc  lamp  has  in  its  crater,  a 


166      ELECTRIC    INCANDESCENT   LIGHTING. 

surface  activity  of,  approximately,  3  KW, 
or  3,000  watts  per  square  centimetre  of  sur- 
face; i.  e.j  19.35  KW  per  square  inch,  or 
27.15  HP  per  square  inch.  This  shows 
that  the  surface  area  of  the  crater  is  very 
small,  since  an  arc  lamp  takes  only  about 
3/5ths  horse-power.  The  apparent  surface 
activity  of  the  sun  is,  approximately, 
10  KW,  or  13.4  HP  per  square  centi- 
metre; i.  e,,  64.5  KW,  or  86.5  HP  per 
square  inch.  Since,  as  we  have  shown,  the 
highest  frequency  of  the  waves  which  are 
emitted  by  a  heated  surface  increases  with 
the  temperature,  it  is  evident  that  the 
highest  frequency  reached  in  the  solar  light 
waves  will  be  greater  than  in  the  arc  light 
waves,  and  this  in  its  turn  will  be  greater 
than  in  the  incandescent  light  waves,  since 
the  intensity  of  surface  activity  in  watts 
per  square  centimetre  differs  so  markedly 
in  these  three  surfaces. 


THE 

Collecting   these    res^ik$^abularly,    we 


Solar  surface  activity,   .     .     .  10,000  watts  pei 
Arc-crater  surface  activity,  .     .  3,000  watts  per  square  cm. 
Incandescing-filament  surface  activity,  70  to  100  watts  per 
square  cm. 

If  the  surface  activity  of  an  incandes- 
cing filament  be  increased,  by  passing  a 
stronger  current  through  the  filament,  that 
is,  by  subjecting  it  to  a  higher  electric 
pressure,  the  temperature  of  the  filament 
will  increase,  and  with  it  the  amount  of 
light  given  off  per  square  centimetre. 
This  increase  may  be  carried  up  to  the 
point  of  destruction  of  the  carbon  fila- 
ment. The  duration  or  life  of  an  incan- 
descing lamp,  depends  very  markedly 
upon  the  temperature  and  surface  activity 
of  the  filament.  At  a  low  temperature, 
or  at  a  dull  red  heat,  an  incandescing  lamp 
will  last  almost  indefinitely ;  at  a  vivid 


168      ELECTRIC   INCANDESCENT   LIGHTING. 

incandescence,  or  very  high  temperature 
and  intense  surface  activity,  its  life  may  be 
only  a  few  minutes.  Between  these  two 
extremes  lies  a  mean  temperature  and  sur- 
face activity,  at  which  it  has  been  found 
in  practice  most  profitable  and  desirable 
to  operate  the  lamp.  The  object,  therefore, 
of  the  lamp  maker  is  so  to  proportion  the 
dimensions  of  the  filament,  that,  when  con- 
nected across  the  mains,  the  surface  activity 
will  reach  the  amount  necessary  to  give 
the  proper  temperature  to  the  filament,  as 
well  as  the  desired  total  quantity  of  light. 

It  should  be  carefully  remembered  that 
the  surface  activity,  which  determines  the 
brightness  of  the  filament,  is  a  quantity 
altogether  distinct  from  the  total- candle- 
power,  or  the  total  quantity  of  light  given 
off  from  the  lamp.  The  brilliancy  depends 
only  on  the  surface  activity,  while  the 


THE   INCANDESCING   LAMP.  169 

total  candle-power  depends  upon  the  total 
surface  area  as  well  as  upon  the  brilliancy. 
It  is  common  to  find  that  a  person  looking 
at  two  lamps,  one  of  which  may  have  a 
high  surface  activity;  i.  e.,  a  great  bril- 
liancy, but  which  only  gives  say  5-candle- 
power,  and  the  other  of  which  has  a  low 
surface  activity,  or  small  brilliancy,  but 
which  gives  16-candle-power,  will  judge 
that  the  brighter  lamp  is  giving  the  greater 
amount  of  light.  In  other  words,  the  eye 
is  very  sensitive  to  relative  brightness  or 
brilliancy,  but  is  by  no  means  sensitive  to 
differences  in  total-candle-power  ;  i.  e.,  total 
intensity  of  the  light.  It  is  very  essential, 
in  all  artistic  groupings  or  arrangements 
of  lamps,  that  their  surface  activity  and 
brilliancy  should  be  as  nearly  equal  as 
possible,  since,  otherwise,  appearing  to  the 
eye  unequally  bright,  they  will  fail  to  pro- 
duce pleasing  effects. 


170      ELECTRIC    INCANDESCENT   LIGHTING. 

Having  given  a  certain  temperature  and 
surface  activity  to  the  filament,  the  total 
amount  of  light  will  depend  upon  the 
total  surface  area.  For  example,  a  16- 
candle-power  lamp,  operated  at  a  given 
temperature,  or  at  an  efficiency  of  say  1/3 
candle-per-watt,  would  take  48  watts  of 
activity.  A  32-caudle-power  lamp,  at  the 
same  brightness,  surface  activity,  and 
quality  of  carbon  filament,  and  therefore, 
with  the  same  efficiency  of  1/3  candle- 
power  per  watt,  would  require  to  be  sup- 
plied with  96  watts  and  would,  therefore, 
require  double  the  surface  from  which  to 
radiate  the  doubled  activity.  Such  a  lamp, 
working  at  the  same  pressure,  would  re- 
quire to  be  both  larger  in  diameter  and 
longer.  Broadly  speaking,  a  lamp  of  high 
candle-power  will  have  a  thick  filament, 
and  a  lamp  of  low  candle-power  a  thin 
filament,  when  working  at  a  common  pres- 


THE   INCANDESCING   LAMP.  171 

sure.  Fig.  48,  represents  the  relative  sizes 
of  incandescent  lamps  of  the  same  manu- 
facture, voltage  and  efficiency,  intended 
for  16,  32,  and  100  candles.  Here  the 
gradually  increasing  lengths  and  diameters 
of  the  filaments  may  be  observed. 

It  may  be  well  to  explain  in  greater 
detail  the  meaning  of  the  term  efficiency, 
as  used  in  the  preceding  paragraph. 
Since  energy  must  be  expended  in  an  in- 
candescing lamp,  in  order  to  produce  a 
certain  candle-power,  it  is  evident,  from 
the  standpoint  of  economy  in  energy,  that 
the  greater  the  number  of  candles  which 
can  be  obtained  per  horse-power,  or  per 
watt  of  activity,  the  greater  will  be  the 
efficiency  of  the  lamp.  We  speak,  there- 
fore, of  the  efficiency  of  an  incandescent 
lamp  as  being  l/3rd  or  l/4th  of  a  candle 
per-watt,  meaning  that  an  8  candle-power 


THE   INCANDESCING   LAMP.  173 

lamp  would  take,  in  either  case,  24  or 
32  watts  respectively,  representing  248.7 
or  186.5  candles  per  electrical  horse-power. 
In  common  usage,  however,  the  term 
efficiency  is  often  unfortunately  misap- 
plied, so  that  the  same  lamps  would  be 
spoken  of  as  having  an  efficiency  of  3  or  4 
watts  per  candle,  respectively,  from  which 
it  would  seem  that  as  we  increase  the  num- 
ber of  watts  to  the  candle  we  increase  the 
efficiency,  whereas,  it  is  evident  that  the 
reverse  is  true.  It  is  preferable,  therefore, 
to  use  the  word  efficiency  in  the  less  popu- 
lar but  more  correct  signification. 

When  an  incandescent  lamp  is  operated 
at  a  constant  pressure,  a  series  of  changes 
takes  place  which  it  is  important  to  follow 
as  closely  as  the  knowledge  we  possess  will 
permit. 

The   temperature    reached   by    the   fila- 


174      ELECTRIC   INCANDESCENT   LIGHTING. 

ment  of  an  incandescing  lamp  has  been 
estimated  from  a  series  of  measurements,  to 
be  in  the  neighborhood  of  1,350°  C.,  slightly 
varying,  however,  with  the  surface  activity 
and  brightness. 

Thus,  at  an  efficiency  of  1/3  candle  per 
watt,  the  temperature  is  estimated  to  be 
1,345°  C. 

At  an  efficiency  of  1/4  candle  per  watt, 
the  temperature  is  estimated  to  be  1,310° 
C. 

And  at  an  efficiency  of  1/4.5  candle  per 
watt,  the  temperature  is  estimated  to  be 
1,290°  C. 

If  we  increase  the  activity  of  an  incan- 
descing lamp  one  per  cent.;  i.  e.,  if  we  in- 
crease the  pressure  at  its  terminals  to  such 
a  point  that  the  number  of  watts  it  re- 
ceives increases  by  one  per  cent.,  the  tem- 
perature is  believed  to  increase  about  2°  C. 


THE  INCANDESCING   LAMP.  175 

and  the   candle-power   is   believed  to   in- 
crease about  three  per  cent. 

When  the  electric  current  passing  through 
a  lamp  produces  the  surface  activity  and 
temperature  for  which  the  lamp  is  de- 
signed, although,  in  general,  the  lamp 
exhibits  a  steady  diminution  in  tempera- 
ture, surface  activity  and  candle-power, 
which  continues  while  the  lamp  is  used,  yet 
it  frequently  happens,  that  for  the  first 
few  hours  these  quantities  actually  in- 
crease, so  that  a  16-candle-power  lamp, 
after  the  first  fifty  hours  of  its  life,  may 
give  17  candles,  and  a  greater  brightness 
than  at  the  start.  Even  when  this  rise 
occurs,  however,  at  the  end  of  the  first 
hundred  hours  the  lamp  will  usually  have 
fallen  in  caudle-power,  brilliancy,  surface 
activity  and  temperature,  all  these  quanti- 
ties being  associated,  to  an  amount  varying 


176      ELECTRIC   INCANDESCENT   LIGHTING. 

with  the  type  of  lamp  and  the  carbon  from 
which  it  has  been  manufactured. 

We  shall  now  examine  the  causes  which 
bring  about  the  progressive  decay  of  the 
lamp  above  referred  to.  When  an  in- 
candescent lamp  is  operated,  it  is  found 
that  the  negative  half  of  the  filament 
throws  off  or  projects  carbon  particles 
from  the  surface,  in  all  directions  in 
straight  lines.  It  is  generally  believed 
that  this  effect  is  due  to  a  species  of 
evaporation.  This  evaporation  takes  place 
with  greatest  activity  near  the  negative 
extremity  of  the  filament,  or  the  point 
where  the  filament  is  united  with  the  lead- 
ing-in  wire  on  the  negative  side.  From 
this  point  of  maximum  evaporation,  the 
effect  diminishes  to  the  centre  of  the  fila- 
ment and  the  positive  side  of  the  filament 
shows  but  little  evaporation.  The  presence 


THE  INCANDESCING   LAMP.  177 

of  electric  evaporation  from  negatively 
charged  surfaces  is  recognized  at  all  tem- 
peratures, and  even  under  atmospheric 
pressures,  but,  like  all  evaporation,  is  aided 
by  a  high  temperature  and  vacuum.  Conse- 
quently, its  effect  is  pronounced  in  an  incan- 
descent lamp.  ' 

The  existence  of  an  evaporation  of  the 
filament  can  be  detected  in  a  variety  of 
ways.  For  example,  if  a  metallic  plate 
be  supported  in  the  lamp  chamber,  mid- 
way between  the  two  legs  of  an  ordinary 
horse-shoe  filament,  it  is  found  that  the 
evaporation  of  the  carbon  particles  from 
the  negative  side  of  the  filament,  is  actually 
capable  of  carrying  an  electric  current  to 
the  plate.  That  is  to  say,  the  stream  of 
negatively  charged  carbon  particles  im- 
pinging against  the  surface  of  the  metallic 
plate,  delivers  up  to  it  the  electricity  with 


178      ELECTRIC   INCANDESCENT   LIGHTING. 

which  they  are  charged  and  so  results  in 
the  passage  of  an  electric  current. 

The  continued  evaporation  of  carbon 
from  the  surface  of  the  filament,  produces 
a  gradually  increasing  blackening  of  the 
surface  of  the  globe,  since  the  projected 
carbon  particles  adhere  to  the  walls  of  the 
chamber  where  they  strike.  The  con- 
tinued bombardment  of  the  glass  walls 
slowly  coats  them  with  a  layer  of  carbon, 
which  being  opaque,  reduces  the  amount 
of  light  emitted  by  the  lamp.  An  old 
lamp,  if  examined  against  a  white  surface, 
such  as  a  sheet  of  paper,  will  be  seen 
to  be  distinctly  blackened  over  its  in- 
terior surface.  This  blackening,  or,  as 
it  is  sometimes  called,  age  coating  of  the 
lamp  chamber,  takes  place,  other  things 
being  equal,  most  rapidly  in  lamps  that 
have  been  burned  at  a  high  tempera- 


THE   INCANDESCING   LAMP.  179 

ture,  since    in    these    the    evaporation   is 
more  rapid. 

Another  proof  that  the  particles  of  car- 
bon leave  the  surface  in  straight  lines  is 
to  be  found  in  the  "shadows"  produced 
on  the  surface  of  the  glass,  when  the 
filaments  are  straight  horse-shoes,  or  lie 
wholly  in  one  plane.  In  such  cases  the 
bombardment  from  any  portion  of  the 
negative  leg  is  necessarily  intercepted  by 
the  positive  leg  in  the  plane  of  the  fila- 
ment, so  that  the  globe  is  protected  in  this 
plane  by  the  interposition  of  the  positive 
leg.  The  result  is,  that  after  the  lamp 
chamber  is  visibly  blackened,  a  distinctly 
marked  line  can  be  traced  on  the  sur- 
face of  the  glass  opposite  the  negative 
leg.  The  term  shadow  is  sometimes  ap- 
plied to  this.  There  will,  however,  be  no 
shadow  on  the  side  of  the  glass  nearest  to 


180      ELECTRIC   INCANDESCENT   LIGHTING. 

the  negative  leg,  nor  will  the  shadow  be 
produced  if  the  polarity  of  the  supply 
mains  is  occasionally  reversed,  or,  in  the 
case  of  lamps  supplied  by  alternating  cur- 
rents where  each  leg  is  positive  and  neg- 
ative alternately. 

Not  only  does  a  lamp  filament  give  less 
light  after  being  operated  at  high  pres- 
sures for  a  considerable  length  of  time, 
owing  to  an  increase  in  its  resistance  and  the 
blackening  of  the  globe,  butialso  to  a  change 
in  the  surface  nature  of  the  filament, 
whereby  it  gives  less  light  for  a  given 
surface  activity.  In  technical  language 
its  emissivity  increases,  so  that  the  tem- 
perature, which  is  attained  by  a  given  sur- 
face activity,  is  reduced.  In  other  words? 
the  lower  the  emissivity  of  a  filament,  the 
higher  the  candle-power  and  brilliancy  for 
a  given  surface  activity.  Of  these  three 


THE   INCANDESCING    LAMP.  181 

causes  for  decreased  candle-power  with  age ; 
namely,  diminished  current  strength  and 
activity,  diminished  translucency  of  the 
globe,  and  increased  emissivity,  the  loss  in 
candle-power  is  about  equally  affected  by 
each. 

Fig.  49  shows  curves  representing  the 
change  in  candle-power  of  an  ordinary 
incandescent  lamp  when  initially  operated 
at  various  efficiencies.  Thus,  at  an  efficiency 
of  0.3  candle-per-watt,  the  lamp  gives  14.5 
candle-power.  At  an  efficiency  of  0.4 
caudle-per-watt,  22.5  candle-power,  and 
at  0.5  candle-per-watt,  32  candle-power. 
Roughly  speaking,  if  we  double  the  effi- 
ciency we  treble  the  candle-power  and 
brilliancy  of  the  lamp.  On  this  account 
it  would  obviously  be  advantageous  to 
increase  the  efficiency  of  a  lamp  as  far  as 
possible. 


182      ELECTRIC   INCANDESCENT   LIGHTING. 


In  the  preceding  diagram  we  have 
plotted  the  relation  between  candle-power 
and  efficiency.  If,  however,  we  plot  the 
relation  between  candle-power  and  activity, 


0.1  0.2  0.3  0.4 

EFFICIENCY.       CANDLES  PER  WATT       /" 


0.5 


FIG.  49. — CURVE  OF  HELATTVE  CANDLE-POWER  OR 
BRIGHTNESS  FOR  A  PARTICULAR  CHARACTER  OF  CAR- 
BON FILAMENT  OPERATED  AT  DIFFERENT  EFFICIENCIES. 


183 

we  find,  rotigid^|^^^^lfiS^  the  candle- 
power  increases  as  the  cube  of  the  activ- 
ity, so  that  if  we  double  the  activity  of 
the  lamp ;  i.  e.,  increase  the  pressure  at  its 
terminals  until  the  product  of  this  in- 
crease of  pressure  and  the  increased  cur- 
rent is  double  what  it  was  originally,  the 
candle-power  of  the  lamp  will  be  in- 
creased about  eight  times,  giving  about 
four  times  as  much  light  per  horse-power 
or  per  watt  expended  in  the  lamp. 

Fig.  50  shows  the  relation,  which  has 
been  experimentally  found  to  exist,  be- 
tween the  average  lifetime  of  lamps  of  the 
same  make  as  that  represented  in  Fig.  49, 
and  the  efficiency  at  which  such  lamps  are 
burned.  A  study  of  this  curve  will  show 
Why  it  is  not,  at  present,  possible  to  obtain 
in  practice  an  efficiency  beyond  a  certain 
value ;  for,  at  an  efficiency  of  0.2  candle- 


184      ELECTRIC    INCANDESCENT   LIGHTING. 


per-watt,  corresponding  to  8  candles  in  the 
particular  lamp  of  Fig.  49,  the  mean  dura- 
tion of  life  is  over  16,000  hours;  while  at 
0.5  candle-per-watt,  corresponding  to  32 


1(5,000 
15,000 


13,000 
12,000 


11,000 
10,000 


9,000 
8,000 


7,000 
6,000 
5,000 


o 

X  4,000 


hi  3,000 


2,000 


1,000 


0  0.1  0.2  0.3  0.4 

EFFICIENCY.     CANDLES  PER  WATT 


FIG.  50. — CURVE  SHOWING  THE  MEAN  DURATION  OP  LIFE 
IN  A  PARTICULAR  CLASS  OF  INCANDESCING  LAMPS  AT 
VARIOUS  EFFICIENCES. 


THE   INCANDESCING   LAMP.  185 

candles  in  Fig.  49,  the  average  duration  of 
life  is  only  100  hours.  In  the  first  case,  we 
should  have  had  an  8-candle-power  lamp 
lasting,  say  18,000  hours,  and  representing  a 
total  output  of  144,000  candle-hours,  while 
in  the  second  case  we  have  a  32-candle- 
power  lamp,  lasting  only  100  hours,  and 
representing  a  total  output  of  3^200  candle- 
hours.  In  the  first  case,  however,  the 
candle-power  would  be  obtained  from  the 
lamp  at  a  comparatively  heavy  expense  in 
energy,  2  1/2  times  more  energy,  in  fact, 
than  that  necessary  for  a  candle  in  the 
second  case.  Moreover,  the  lamp  in  the 
first  case  would  be  very  dull  in  color  and 
unpleasant  to  the  eye. 

Between  the  above  two  extremes  of 
long  life  and  low  efficiency,  and  short  life 
and  higli  efficiency,  there  exists  a  certain 
mean  value  most  suitable  for  commercial 


186      ELECTRIC   INCANDESCENT   LIGHTING. 

purposes.  This  mean  value,  as  lamps  are 
now  constructed,  is  in  the  neighborhood  of 
0.3  candle-per-watt,  representing  an  aver- 
age life  time  of  2,000  hours.  This  dura- 
tion must,  however,  only  be  considered  as 
the  average  lifetime,  since  it  frequently 
happens  that  among  a  number  of  lamps 
manufactured  by  the  same  process,  and 
with  equal  skill,  some  may  only  last  about 
100  hours  at  this  efficiency,  while  others 
may  greatly  exceed  2,000  hours. 

With  any  installation  of  electric  lamps, 
it  lies,  therefore,  in  the  power  of  the 
engineer  in  charge  of  the  plant,  to  so  oper- 
ate the  lamps  that  their  life  may  be  bril- 
liant but  short,  or  dull  but  long;  as 
will  depend  entirely  upon  the  pressure 
maintained  at  the  lamp  terminals.  Thus, 
if  a  16-candle-power  incandescent  lamp, 
intended  for  an  activity  of  50  watts,  at  115 


THE   INCANDESCING   LAMP.  187 

volts,  and  therefore,  to  be  operated  at  a 

1  (\ 

normal  activity  of  —  or   0.32    candle-per- 
ou 

watt,  be  steadily  operated  at  a  pressure 
one  volt  in  excess,  or  116  volts,  its  initial 
candle-power  will  be  raised  to  17  candles, 
but  its  lifetime  will  be  abbreviated  about 
seventeen  per  cent.  Again,  if  the  pressure 
be  steadily  maintained  at  2  volts  excess,  or 
117  volts,  the  initial  candle-power  will  be 
normally  18  candles,  but  the  probable  life- 
time  will  be  reduced  about  thirty-three  per 
cent. 


When  lamps  are  placed  in  somewhat 
inaccessible  positions,  such  as  near  the  ceil- 
ings of  high  halls,  where  there  is  some 
inconvenience  in  reaching  them,  it  becomes 
particularly  objectionable  to  have  to  renew 
these  lamps  too  frequently.  In  order  to 
avoid  this,  the  plan  is  sometimes  adopted 


188      ELECTRIC   INCANDESCENT   LIGHTING. 

of  operating  the  lamps  at  a  comparatively 
low  efficiency  and  brilliancy,  thus  necessi- 
tating some  extra  expense  in  power,  but 

greatly  prolonging  the  average  lifetime. 

t 

Fig.  51  represents  the  rate  of  variation 
of  candle-power  in  similar  samples  of  the 
same  type  of  lamp  when  operated  at  dif- 
ferent steady  pressures.  Curve  No.  5  rep- 
resents a  108-volt,  1 6-candle-power  lamp 
of  0.286  candle-per-watt  normal  efficiency, 
operated  at  108  volts.  The  candle-power 
slightly  rises  to  about  16.6  candles,  in  90 
hours,  and  finally  falls  to  11  candles  after 
500  hours.  The  efficiency  of  the  lamp  at 
this  time  will,  of  course,  be  materially 
reduced. 

Curve  No.  4  of  Fig.  51,  represents  the 
behavior  of  a  similar  lamp  operated  at  110 
volts  pressure.  Here  the  initial  candle- 


THE   INCANDESCING  LAMP. 


189 


power  is  raised  to  17  1/2  candles  and  after 
500  hours  burning,  the    candle-power    is 


200  300 

HOURS 


Fm.  51. — CURVES  OP  CANDLE-POWER  IN  LAMPS  OF  SAME 
TYPE  OPERATED  AT  DIFFERENT  FIXED  EFFICIENCIES. 

about  10  3/4  candles.     Curve  No.  3  shows 
similar  results  for  a  pressure  of  112  volts. 


190      ELECTRIC   INCANDESCENT  LIGHTING. 

Curve  No.  2  for  113  volts  and  Curve  No. 
1  for  114  volts.     Here  the  candle-power 


\ 


100  200  300  400  600  600  700  HOO  900 

HOURS 

FIG.  52.— CURVES  OP  CANDLE-POWER  OP  THE  SAME  TYPES 
OP  LAMP  OPERATED  AT  DIFFERENT  EFFICIENCES. 


commences  at  24,  but  is  less  than  14  after 
200  hours. 


Fig.  52  represents  the  behavior  of  four 
similar  types  of  lamps,  operated    steadily 


THE   INCANDESCING   LAMP.  191 

at  various  efficiencies,  instead  of  at  various 
pressures.  Curve  No.  1,  represents  the 
behavior  with  0.25  candle-per-watt ;  Curve 
No.  2,  0.286  candle-per-watt;  Curve  No.  3, 
0.333,  and  curve  No.  4,  0.4  candle-per- 
watt.  It  will  be  seen  that  the  high  effi- 
ciency lamp  falls  to  fifty  per  cent,  of  its 
initial  candle-power  in  600  hours,  while 
the  lowest  efficiency  lamp  only  loses  ten 
per  cent,  of  its  candle-power  in  the  same 
time. 

It  is  evident,  therefore,  that  no  matter 
what  the  initial  efficiency  of  a  lamp  may 
be,  a  time  will  come  in  its  life  when  its 
efficiency  must  be  low.  When  this  point 
is  reached,  the  amount  of  activity  absorbed 
by  the  lamp,  at  constant  voltage,  is  less 
than  it  was  at  the  outset,  seeing  that  the 
resistance  of  the  attenuated  filament  is 
increased.  On  the  other  hand,  the  effi- 


192      ELECTRIC   INCANDESCENT  LIGHTING. 

ciency,  or  candles-per-watt,  has  diminished, 
and  as  regards  its  light,  the  electric  power 
is  more  wastefully  applied.  It  becomes, 
therefore,  a  question  whether  it  would  not 
be  advisable  to  discard  or  break  the  lam}), 
and  replace  it  by  a  new  one,  having  a 
greater  efficiency.  By  so  doing  we  incur 
the  expense  of  a  new  lamp  earlier  than 
if  we  waited  for  the  old  lamp  to  break 
naturally,  but  we  utilize  the  power  of  the 
central  station  more  economically. 

The  question  of  the  smashing  point  of  a 
lamp,  or  the  point  in  the  life  of  a  lamp  at 
which  it  may  be  deemed  more  economical 
to  replace  it  by  a  new  one,  or  its  economical 
age,  may  be  considered  from  three  distinct 
standpoints  ;  namely  : 

(1)  From   the    central-station    point   of 
view. 

(2)  From  the  consumer's  point  of  view. 


THE   INCANDESCING   LAMP.  193 

(3)  From  the  isolated-plant  point  of 
view. 

The  central  station  has  usually  to  re- 
place broken  or  useless  lamps,  and  since 
the  charge  for  service  is  based  upon  the 
ampere-hour,  or  the  watt-hour,  so  long  as 
the  lamps  burn  and  the  consumer  is  fairly 
satisfied,  the  smashing  point  may  be  indef- 
initely extended.  It  is  to  the  station  man- 
ager's advantage,  however,  to  maintain  a 
steady  pressure  over  the  system  of  mains, 
so  that  the  lamps  are  not  forced  above 
candle-power  and  their  lives  unduly 
abridged.  In  the  best  central  stations 
great  care  is,  therefore,  always  taken  that 
the  pressure  is  maintained  as  closely  as 
possible  to  the  normal.  Should  the  pres- 
sure become  markedly  increased,  the  cost 
of  renewing  lamps  will  be  rapidly  aug- 
mented. Should  it  become  markedly 


194      ELECTRIC    INCANDESCENT  LIGHTING. 

diminished,  the  consumers  would   be  dis- 
satisfied. 


From  the  consumer's  point  of  view  the 
lamps  would  require  to  be  operated  at  a 
high  efficiency  regardless  of  their  lifetime, 
since  he  would  thus  obtain,  from  the  power 
for  which  he  pays,  the  highest  brilliancy 
and  the  maximum  quantity  of  light.  More- 
over, lamps  which  will  not  break  before 
becoming  seriously  dulled,  thus  necessitat- 
ing their  renewal,  are  a  disadvantage. 
From  the  standpoint  of  the  consumer,  there- 
fore, the  smashing  point  of  a  lamp  is  reached 
as  early  as  possible,  or  at  the  opposite  ex- 
treme to  that  of  the  station  manager. 

From  the  standpoint  of  the  owner  of  the 
isolated  plant,  who  is  both  producer  and 
consumer,  the  smashing  point  will  neces- 
sarily occupy  some  intermediate  position; 


195 

Desires  to 
light  for  the 
activity  produced  or  coal  consumed,  on  the 
other  hand  he  wishes  to  reduce  the  cost  of 
lamp  renewals  as  far  as  possible.  No  pre- 
cise rule,  however,  can  be  laid  down. 

There  are  in  general,  two  purposes  for 
which  light  is  ordinarily  employed  ;  namely, 
for  actual  use,  as  in  reading,  or  other  work, 
and  for  the  aesthetic  purposes  of  ornamen- 
tation. Regarding  the  latter  purpose  as 
a  luxury,  lamps  may  be  changed  as  often 
as  taste  may  dictate,  but  high-efficiency, 
high-brilliancy,  short-lived  lamps  will  be 
preferable.  On  the  other  hand,  so  long  as 
a  lamp  fulfills  the  utilitarian  purpose  of 
enabling  work  to  be  conveniently  and 
healthfully  performed,  it  is  waste  of  money 
to  throw  the  lamp  away.  The  smashing 
point,  therefore  of  lamps  intended  to 


196      ELECTRIC   INCANDESCENT  LIGHTING. 

illumine  working  rooms  depends  largely 
upon  the  total  candle-power  installed.  If 
this  is  ample  in  the  first  instance,  a  very 
considerable  falling  off  in  candle-power 
may  be  permitted  without  interfering  with 
the  usefulness  of  the  light,  and  economy  is 
rarely  pushed  to  such  a  degree  as  to  limit 
closely  the  candle-power  installed  for  pur- 
poses of  reading  or  working. 

It  is  found,  however,  that  in  central 
station  practice  the  best  commercial  results 
are  secured  with  ample  satisfaction  to  the 
consumers,  if  the  efficiency  at  which  the 
lamps  are  operated  on  the  system,  is  such 
that  the  cost  of  lamp  renewals  is  approx- 
imately fifteen  per  cent,  of  the  total  opera- 
ting expenses  of  the  station.  Where  the 
pressures  between  the  mains  can  be  closely 
regulated,  it  is  preferable  to  employ  high- 
efficiency  lamps,  but  where  the  reverse  is 


THE   INCANDESCING   LAMP.  197 

the  case,  low-efficiency  lamps  are  desirable, 
since  a  low-efficiency  lamp  can  stand  an 
accidental  increase  in  pressure  with  less 
detriment  to  its  length  of  life  than  a  high- 
efficiency  lamp  ;  for,  being  normally  oper- 
ated at  a  lower  temperature,  an  increase  of 
temperature  may  not  be  dangerous. 


CHAPTER  X. 

LIGHT    AND    ILLUMINATION. 

THERE  are  two  technical  words  which 
are  very  apt  to  be  confused  in  their 
meaning,  and  misused  in  their  applica- 
tion; namely,  " light "  and  "illumination." 
When  correctly  used,  the  word  light  signi- 
fies the  flow  or  flux  of  light  emitted  by  a 
luminous  source,  irrespective  of  the  sur- 
face on  which  it  falls,  while  the  word 
illumination  means  the  quantity  of  light 
received  on  a  surface,  per  unit  of  area, 
whether  received  directly  from  the  lumin- 
ous source,  or  indirectly  by  diffusion  and 
reflection  from  surrounding  bodies.  The 
words  "  light "  and  "  illumination  "  are  unf  or- 


198 


LIGHT   AND   ILLUMINATION.  199 

tunately  often  used  synonymously,  whereas 
it  is  evident  that  they  denote  distinct 
ideas. 

By  the  candle-power  of  a  source  of  light, 
we  mean  the  luminous  intensity  of  the 
source  as  measured  in  units  of  luminous 
intensity.  The  unit  of  luminous  intensity, 
commonly  employed,  is  the  British  candle, 
and  is  equal  to  the  intensity  of  light  pro- 
duced by  a  candle  of  definite  dimensions 
and  composition,  burning  at  the  rate  of  2 
grains,  or  0.1296  gramme,  per  minute.  If 
we  speak  of  a  source  of  light  as  having, 
say  a  luminous  intensity  of  20  British 
standard  candles,  we  mean  that  if  that 
source  were  reduced  to  a  mere  point,  it 
would  yield  as  much  light  as  20  standard 
candles  all  concentrated  at  a  single  point. 

A  standard  of  luminous  intensity  very 


200      ELECTRIC   INCANDESCENT   LIGHTING. 

generally  adopted,  except,  perhaps,  in 
English-speaking  countries,  is  the  Frencli 
standard  candle,  called  the  bougie-decimale, 
or  the  1/2 Oth  of  the  intensity  of  an 
international  standard  unit  called  the 
Viotte.  The  Violle  is  a  unit  of  lumin- 
ous intensity  produced  in  a  perpendicular 
direction,  by  a  square  centimetre  of  plati- 
num, at  the  temperature  of  its  solidifi- 
cation. The  British  standard  candle  is 
slightly  in  excess  of  the  bougie-decimale, 
one  British  candle  according  to  Everett 
being  1.012  bougie-decimale. 

If  we  imagine  a  point  source  of  light,  of 
unit  intensity ;  i.  e.,  one  standard  French 
candle,  or  bougie-decimale,  to  be  placed  at 
the  centre  of  a  hollow  sphere,  of  the  radius 
of  one  metre,  or  39.37",  then  the  total 
internal  surface  of  the  sphere  will  receive 
a  definite  total  quantity  of  light.  Each 


gJiBBttfljggs. 

c^X  ffy' 

4   PROPERTY  OF    1JI9 

yMGHT   AND    ILLUMINATION.  ^'//  201 

»V4b 

unit  of 

spherical  nrimTTpwffl-TT^^  unit  of 

light ;  and,  since  the  total  interior  surface 
of  such  a  sphere  contains  4  X  3.1416  = 
12.566  square  metres,  the  total  quantity  of 
light  received  on  the  interior  surface  will 
be  12.566  units,  called  lumens.  Conse- 
quently, if  a  point  source  of  unit  intensity 
emits  12.566  lumens,  a  source,  of  say  20 
bougie-decimales,  would  yield  an  intensity 
of  251.32  lumens. 

It  is  obviously  not  necessary  that  the 
surface,  which  surrounds  the  unit  point 
source,  should  be  spherical.  The  same 
amount  of  light;  namely,  12.566  lumens, 
will  be  given  off  by  the  source  independ- 
ently of  the  shape  of  the  receiving  surface, 
so  that  when  such  a  source  is  placed,  for 
example,  alone  in  a  room,  the  total 
quantity  of  light  which  falls  directly  upon 


202      ELECTRIC    INCANDESCENT   LIGHTING. 

the  walls,  ceiling  and  floor  of  the  room- 
from  the  source,  will  be  12.566  lumens. 
This  will  be  true  in  fact  if  there  are  other 
sources  of  light  in  the  room  at  the  same 
time.  The  quantity  of  light  which  each 
point  source  will  emit  will  be  12.566 
times  its  luminous  intensity. 

If  one  lumen  falls  perpendicularly  and 
uniformly  over  the  surface  of  one  metre, 
the  illumination  of  that  surface  will  be 
one  lux,  the  lux  being  the  unit  of  illumi- 
nation. If,  for  example,  a  bougie-decimale 
is  located  at  the  centre  of  a  sphere  of  one 
metre  radius,  then  each  square  metre  of 
the  interior  surface  of  the  sphere  will 
receive  one  lumen  of  light,  and  this  light 
falls  everywhere  perpendicularly  upon  its 
surface.  The  illumination  on  the  interior 
surface  is  everywhere  one  lux.  A  bougie- 
decimale  produces,  therefore,  when  acting 


LIGHT   AND   ILLUMINATION.  203 

alone,  an  illumination  of  one  lux  at  a  dis- 
tance of  one  metre. 

The  mistake  is  not  infrequently  made, 
that  because  a  surface  receives  light 
directly  from  a  given  source  of  known 
intensity,  its  illumination  can  be  deter- 
mined by  mere  calculation  of  its  distance 
from  the  source.  It  must  be  remembered 
that  it  also  receives  reflected  or  diffused 
light  from  all  neighboring  surfaces,  which, 
consequently,  tend  to  increase  its  illumina- 
tion. 

The  law  of  illumination  from  a  single 
point  source,  acting  alone ;  i.  e.,  in  a  space 
where  all  reflected  or  other  light  is  ex- 
cluded, is  that  the  illumination  varies 
inversely  as  the  square  of  the  distance 
from  the  source.  Thus,  we  know  that  a 
bougie-decimale  produces  an  illumination 


204      ELECTRIC    INCANDESCENT   LIGHTING. 

of  one  lux  upon  a  surface  held  perpen- 
dicularly to  the  rays  of  light  at  a  distance 
of  one  metre.  If  the  surface  be  held  at 
a  distance  of  2  metres  from  the  point 
source,  in  a  room  otherwise  dark,  the 
illumination  will  be  l/4th  of  a  lux,  or 
(l/2)a ;  at  a  distance  of  3  metres  the 
illumination  would  be  similarly  l/9th  lux, 
or  (1/3)2.  Generally,  a  point  source,  of  say 
50  bougie-decimales,  would  produce,  at  a 
distance  of  say  5  metres,  an  illumination  of 

50 

-^  =  2  luxes. 

In  practice,  if  a  surface  were  placed  in 
a  room  at  a  distance  of  5  metres  from 
a  source  of  50  bougie-decimales,  the  illu- 
mination received,  if  the  rays  be  allowed 
to  fall  perpendicularly  upon  the  surface, 
will  be  more  than  2  luxes,  because  this 
amount  of  illumination  will  be  produced 


LIGHT    AND   ILLUMINATION.  205 

by  the  direct  action  of  the  source  in  a 
space  from  which  all  other  light  was  ex- 
cluded, whereas,  reflection  from  the  walls 
of  the  rooms,  mirrors,  ceilings,  etc.,  will 
increase  this  amount  of  illumination  to, 
perhaps,  10  luxes,  and,  if  it  were  possible 
to  have  the  surfaces  of  the  walls  perfectly 
reflecting,  the  illumination  which  would 
be  produced  in  all  parts  of  the  room 
would  be  indefinitely  great.  Conse- 
quently, the  amount  of  illumination 
received  upon  the  surface  of  a  desk  or 
table,  depends  not  only  upon  the  number 
of  lamps  in  a  room,  on  their  candle-power 
and  arrangement,  but  also  upon  the  char- 
acter of  the  surfaces  of  the  walls  and 
furniture.  Therefore,  the  question  of 
lighting  a  room  is  not  altogether  a  ques- 
tion of  its  dimensions  and  of  the  total 
candle-power  placed  in  it,  but  also  depends 
upon  the  arrangement  of  the  lamps,  and 


206      ELECTRIC   INCANDESCENT   LIGHTING. 

the  character  of  the  decoration  and  furni- 
ture, and  the  nature  of  their  reflecting 
surfaces. 

The  illumination  required  for  comfort- 
able reading  is  from  15  to  25  luxes  on 
the  surface  of  a  printed  page.  Any 
illumination  less  than  10  luxes  is  fati- 
guing, if  long  continued.  The  illumina- 
tion produced  by  full  moonlight  is  about 
l/8th  lux,  and  that  by  full  sunlight 
80,000  luxes.  The  illumination  in  a 
street  as  ordinarily  lighted  by  arc  lamps, 
is,  perhaps,  50  luxes  near  the  ground 
below  an  arc  lamp,  and  about  1  lux 
near  the  ground  midway  between  the 
lamps. 

The  luminous  intensit}^  of  an  incan- 
descent lamp  is  not  the  same  in  all  direc- 
tions, owing  to  the  fact  that  the  filament 


is  not  a 
positions, 

is  exposed  th  n TTtff-nttiTrry — JffiffTn  simph 
horse-shoe  filament,  with  both  legs  in 
one  plane,  gives  less  light  in  this  plane 
than  in  any  other  plane  passing  through 
the  vertical,  because  each  leg  intercepts 
the  light  from  the  other.  The  mean 
spherical  candle-power  of  a  lamp,  in  bou- 
gie-decimales,  is  the  quantity  of  light  it 
emits  in  lumens,  divided  by  12.566.  In 
other  words,  the  mean  spherical  candle- 
power  of  a  lamp  is  the  equivalent  point 
source  which  emits  as  much  light  in  all 
directions  as  the  actual  lamp  does. 
The  spherical  candle-power  of  an  incan- 
descent lamp  is  usually  about  twenty  per 
cent,  less  than  its  maximum  horizondl  in- 
tensity, so  that  when  we  speak  of  a  16- 
candle-power  lamp,  a  point  source  of  about 
13  candles  intensity  would  supply  the  same 


208      ELECTRIC    INCANDESCENT   LIGHTING. 

total  number  of  lumens  as  is  emitted  from 
the  actual  lamp.  A  point  source  would 
Lave  no  base  or  socket  and  would  disperse 
light  equally  in  all  directions. 

It  may  be  of  interest  to  note  that  a 
lux-second,  that  is  to  say,  the  total  time- 
illumination  produced  by  one  lux  for  one 
second  of  time,  has  been  accepted  by  the 
International  Photographic  Congress  of 
Brussels  as  the  unit  of  time-illumination, 
under  the  name  of  the  pilot.  A  phot  is 
a  lux-second,  and  is  a  unit  of  time  illumina- 
tion employed  in  photography.  It  is  well 
known  in  photography  that  the  actinic 
effect  of  light,  that  is  its  power  of  effect- 
ing chemical  decomposition  as  utilized  in 
photography,  depends,  for  a  given  quality 
of  light,  both  on  its  intensity  and  on  the 
duration  of  its  action.  In  photography, 
therefore,  this  practical  unit  was  required 


LIGHT   AND    ILLUMINATION.  209 

to  represent  tlie  product  of   illumination 
and  time. 

The  caudle-power  of  incandescent  lamps 
varies  from  1/2  candle  up  to  100  British 
Standard  candles,  although  both  larger 
and  smaller  candle-powers  have  been 
specially  prepared.  The  16-candle-power 
lamp  is  generally  employed  in  the  United 
States,  and  the  10-candle-power  lamp  is 
generally  employed  in  Europe.  The  sizes 
usually  manufactured  are  1/2,  1,  2,  3,  4,  5, 
6,  8,  10,  16,  20,  32,  50,  60  and  100. 


CHAPTER  XI. 

SYSTEMS    OF   LAMP    DISTRIBUTION. 

BROADLY  speaking,  there  are  two  gen- 
eral methods  by  means  of  which  lamps 
may  be  connected  with  a  generating  source 
of  electricity ;  namely,  in  series,  so  that 
the  current  passes  successively  through 
each  lamp  before  it  returns  to  the  source, 
and  in  multiple  or  parallel;  so  that 
the  current  divides  and  a  portion  passes 
through  each  lamp. 

Fig.  53,  represents  three  lamps  con- 
nected in  series,  and  Fig.  54,  represents 
three  lamps  connected  in  parallel.  In  the 
case  of  the  series  connection  shown  in  Fig. 


210 


SYSTEMS   OF   LAMP   DISTRIBUTION.        211 

53,  the  three  lamps  are  so  connected  that 
the  current  from  the  source,  entering  the 
line  at  +,  flows  in  the  direction  indicated 
by  the  arrows,  passes  successively  through 
the  lamps  A,  B,  and  C\  returning  to  the 


FIG.  53.— SERIES-CONNECTED  LAMPS. 

source  at  the  negative  end  of  the  line.  In 
Fig.  54,  the  three  lamps  A,  B,  Cf,  are  con- 
nected as  shown,  to  the  positive  and  nega- 
tive leads  respectively,  and  the  current 
passes  through  them  in  the  direction  indi- 
cated by  the  arrows.  The  arterial  system 
of  the  human  body  furnishes  an  example 


212      ELECTRIC   INCANDESCENT   LIGHTING. 


of  a  parallel  or  multiple  system,  since  the 
blood  flow  divides  into  a  very  great  num- 
ber of  different  channels  or  capillaries, 
and,  after  passing  through  these  independ- 


FIG.  54. — MULTIPLE-CONNECTED  LAMPS. 

ent   channels,  finally  unites   in   the    veins 
and  returns  to  the  heart. 

In  order  to  compare  the  relative  advan- 
tages of  the  series  and  multiple  methods 
of  electric  distribution,  let  us  suppose  that 
a  house  has  to  be  lighted  electrically  at  a 
distance  of  a  mile  from  the  dynamo,  and 
that  for  this  purpose  an  amount  of  light 
represented  by  1,000  candles  is  required, 


SYSTEMS   OF   LAMP   DISTRIBUTION.        213 

distributed  in  50,  20-candle-power  lamps. 
Further,  let  us  assume  that  the  same 
efficiency  is  secured  in  the  operation  of 
these  lamps,  whatever  system  we  may 
adopt,  or  whatever  dimensions  the  lamp 
filament  may  take,  a  supposition  in  accord- 
ance with  general  practice.  Let  us  sup- 
pose that  this  efficiency  will  be  1/4  candle 
per  watt.  We  shall  then  require  to  ex- 
pend 4,000  watts  of  electric  energy  in  the 
lamp  filaments  in  the  house.  This  amount 
of  activity  might  be  electrically  expended 
in  a  great  variety  of  ways,  as  regards  the 
pressure  and  current  of  delivery,  but  it 
will  suffice  to  compare  two  ways  only; 
namely,  the  delivery  of  4  amperes  at  a 
pressure  of  1,000  volts,  and  the  delivery 
of  1,000  amperes,  at  a  pressure  of  4  volts. 
In  each  of  these  two  cases  the  activity 
delivered  will  be  the  same;  namely  4 
KW. 


214      ELECTRIC   INCANDESCENT  LIGHTING. 

If  it  be  required  to  expend  only  1,000 
watts  in  the  main  conductors  carrying  the 
current  to  the  house,  when  all  the  lamps 
are  turned  on,  5,000  watts  or  5  KW  will 
have  to  be  supplied  at  the  generator  termi- 
nals, of  which  twenty  per  cent.,  or  1,000 
watts,  is  permitted  to  be  lost  in  transmis- 
sion in  the  leads,  as  heat.  We  know  that 
this  loss  will  be  the  product  of  the  current 
strength  and  the  drop  in  volts  in  the  two 
conductors.  In  the  first  plan  of  1,000 
volts  and  4  amperes  at  the  house,  the  drop 
of  pressure  in  the  two  wires  must  be  250 
volts,  in  order  that  250  volts  X  4  am- 
peres =  1,000  watts,  so  that  the  resistance 
of  the  two  wires  together,  which  shall 
produce  a  drop  of  250  volts,  with  a  cur- 
rent of  4  amperes,  will  be  62  1/2  ohms,  or 
31  1/4  ohms  to  each  wire  one  mile  in 
length.  The  nearest  size  of  wire  to  that 
which  has  a  resistance  of  31  1/4  ohms  to 


SYSTEMS   OF   LAMP   DISTRIBUTION.        215 

the  mile,  is,  No.  18  B.  &  S.  or  A.  W.  G., 
having  a  diameter  of  0.0403",  or,  approxi- 

mately, the  ^th  of  ail  inch.     Such  a  wire 
2f) 

would  weigh  about  26  Ibs.  and  the  two 
wires  forming  the  complete  circuit  would 
weigh  about  52  Ibs. 

Considering  the  second  plan  of  4  volts 
and  1,000  amperes,  the  drop  in  the  wires 
would  have  to  be  only  one  volt.  In  order 
that  the  activity  expended  in  them  should 
be  1  KW  since  1  volt  x  1,000  amperes  = 
1  KW  the  resistance  in  the  two  wires 
together,  to  permit  of  a  drop  of  but  1 

volt  with  1,000  amperes,  must  be     / 
of  an  ohm,  since  1,000  amperes  x 


ohm  =  1  volt.     The  two  wires   together 
must,  therefore,  have  a  resistance  of 


216      ELECTRIC   INCANDESCENT   LIGHTING. 

ohm,  or   each  must  have  a  resistance  of 
— th  ohm.     A  wire  which  would  have 

this  resistance  would  have  62,500  times 
the  cross-section  and  weight  of  the  wire  in 
the  preceding  case ;  so  that,  instead  of  re- 
quiring 52  Ibs.  of  copper,  in  all,  for  the 
two  miles  of  conductor,  we  should  require 
approximately  3,250,000  Ibs.,  or  1,625 
short  tons  of  copper. 

It  is,  therefore,  evident  that  although  a 
given  electric  activity  can  be  expended  in 
incandescent  filaments  either  at  a  high 
pressure  or  at  a  low  pressure,  the  advan- 
tage of  a  high  pressure  is  very  great,  when 
the  power  is  to  be  transmitted  electrically 
to  a  distance.  If  we  double  the  pressure 
of  transmission ;  i.  e.,  if  we  double  the 
number  of  volts  between  the  two  main 
conductors,  we  require  four  times  less  cop- 


SYSTEMS   OF   LAMP   DISTKIBUTION.        217 

per  for  a  given  percentage  of  loss  of 
activity  in  them.  Thus,  in  the  preceding 
case,  when  we  increased  the  pressure  of 
delivery  from  4  volts  to  1,000  volts,  we 
increased  it  250  times,  and,  therefore,  wre 
diminished  the  amount  of  copper  which 
was  required  for  twenty  per  cent,  loss,  250 
X  250  or  62,500  times.  Consequently,  the 
first  essential  for  economical  distribution 
of  electric  power  to  a  distance,  either  for 
lamps,  or  for  any  other  purposes,  is  high 
electric  pressure  of  delivery. 

If  then  we  adopt  provisionally,  the  plan 
of  supplying  the  house  above  considered 
at  a  pressure  of  1,000  volts  and  4  am- 
peres, this  would  appear  to  be  most  readily 
carried  out  at  first  sight,  by  connecting 
50  lamps  in  a  single  series  through  the 
house,  each  lamp  being  intended  for  20 
volts  and  4  amperes.  When  all  the  lamps 


218      ELECTRIC   INCANDESCENT   LIGHTING. 

are  lighted,  the  total  current  would  be  4 
amperes,  when  the  total  pressure  of  de- 
livery amounted  to  50  x  20,  or  1,000  volts. 
Though  such  a  system  could,  doubtless,  be 
installed,  yet  it  would  possess  several  dis- 
advantages. In  the  first  place,  unless  some 
device  were  provided  whereby  a  faulty 
lamp  became  automatically  short-circuited, 
the  failure  of  any  single  lamp  would 
interrupt  the  entire  circuit  and  extinguish 
all  the  other  lamps.  Moreover,  the  pres- 
sure which  would  have  to  be  supplied  to 
the  house  between  the  main  conductors 
would  depend  upon  the  number  of  lamps 
employed.  When  a  single  lamp  only  was 
lighted,  the  pressure  required  would  be  20 
volts  and  the  current  4  amperes.  This 
would  mean  that  the  generating  dynamo 
in  the  station  supplying  the  house  could 
only  be  used  for  that  particular  house, 
since,  if  two  houses  were  supplied  from 


SYSTEMS   OF   LAMP   DISTRIBUTION.        219 

the  same  dynamo,  one  might  have  all  the 
lamps  turned  on  and  thus  require  1,000 
volts  and  4  amperes,  while  the  other 
might  have  only  half  its  lamps  turned  on, 
thus  requiring  500  volts  and  4  amperes. 
For  this  and  other  reasons  it  is  now  uni- 
versally considered  that  incandescent  light- 
ing on  any  extended  scale  must  necessarily 
be  conducted  by  a  multiple-arc  system. 

It  would  be  practically  impossible  to 
construct  incandescent  lamps  capable  of 
being  operated  in  parallel  at  the  pressure 
of  1,000  volts  assumed  in  this  case;  for, 

each  lamp  would   have  to  be  capable  of 

4 
taking  a   current   of  — ths   ampere,   at   a 

pressure  of  1,000  volts.  The  resistance 
would  have  to  be  12,500  ohms  hot,  so  that 
the  filament  would  have  to  be  very  fine 
and  long.  Such  a  lamp  would  be  quite 


220      ELECTRIC    INCANDESCENT   LIGHTING. 

impracticable,  and,  moreover,  the  pressure 
of  1,000  volts  is  •  not  considered  safe  to 
introduce  into  a  building.  The  maximum 
pressure  for  which  it  has  been  possible, 
until  recently,  to  construct  incandescent 
lamps  has  been  120  volts,  so  that  incandes- 
cent lighting  between  a  single  pair  of 
conductors  has  been  practically  limited  to 
a  pressure  of  115  volts  at  the  lamp 
terminals. 

The  lack  of  economy  of  11 5- volt  pres- 
sures for  incandescent  lighting  at  a  dis- 
tance, as  regards  the  amount  of  copper 
required,  was  early  apparent,  and  a  method 
was  invented  and  introduced  which  is 
practically  a  compromise  between  the 
series  and  parallel  systems ;  that  is  to  say 
a  method  was  invented  whereby  the  ad- 
vantages of  the  parallel  connection  of 
lamps  were  secured,  together  with  the 


SYSTEMS   OF   LAMP   DISTRIBUTION.        221 

advantage  of  higher  pressure  obtained  by 
coupling  lamps  in  series.  This  method  is 
fundamentally  what  is  called  a  series-mul- 
tiple system,  and  in  practice  is  what  is 
generally  called  the  three-wire  system. 

A  + 


c—  c 

FIG.  55. — THREE- WIRE  SYSTEM,  SERIES-MULTIPLE  CON- 
NECTION. 

The  three-wire  system  is  illustrated  in 
Fig.  55.  Here  there  are  two  multiple-arc 
circuits,  one  between  the  mains  A  and  B, 
and  the  other  between  the  mains  B  and  C. 
Between  each  of  these  pairs  of  mains  the 
pressure  is  115  volts,  supplied  by  a  sepa- 
rate dynamo  as  shown.  The  positive 
terminal  of  the  dynamo  D2,  being  con- 


222      ELECTRIC   INCANDESCENT  LIGHTING. 

nected  to  the  negative  terminal  of  $  the 
dynamo  Dly  it  is  evident  that  between  the 
mains  A  A  and  C  C,  there  will  be  a  pres- 
sure of  230  volts.  In  the  case  shown 
there  are  12  lamps  in  all,  or  6  on  each 
side  of  the  system,  so  that  about  3 
amperes  will  be  flowing  through  the  mains 
A  A  and  C  O,  and  no  current  will  pass 
through  the  neutral  conductor  B  B.  If 
the  number  of  lamps  on  the  two  sides  of 
the  system  be  unequal,  the  difference  be- 
tween the  current  strengths  will  return 
by  the  neutral  conductor ;  for  example, 
if  all  the  lamps  between  B  and  C,  are 
turned  off,  3  amperes  will  flow  along  the 
positive  main  A  A,  and  return  by  the 
neutral  main  B  B,  no  current  passing 
through  the  negative  main.  Since,  on  the 
average,  when  the  Aviring  is  judiciously 
carried  out,  the  loads  on  the  two  sides  of 
the  system  will  usually  nearly  balance  each 


223 

other, ^^^ei^tjral  conelucton^ifjxjpfily  have 
to  carry  ast^afli^ua^oi^f^Te  current  in 
the  outside  mains,  and  may  therefore  be 
much  lighter.  If  the  neutral  conductor 
could  be  entirely  dispensed  with,  we 
know  that  the  copper  required  to  sup- 
ply the  system  with  a  given  percentage  of 
loss  in  transmission  would  be  four  times 
less  on  the  three-wire  system,  than  on 
the  two-wire  system,  since  the  pressure 
of  distribution  would  be  doubled.  The 
three-wire  system  would,  therefore,  ensure 
a  saving  of  seventy -five  per  cent,  in  the 
amount  of  copper  required  for  the  mains. 
In  practice,  however,  the  amount  of  copper 
in  the  neutral  conductor  averages,  over 
an  entire  system,  about  sixty  per  cent, 
of  that  in  the  outside  conductor,  so  the 
neutral  is  made  a  little  more  than  half 
as  heavy  as  either  of  the  outside  mains. 
Under  these  conditions,  the  actual  saving 


224      ELECTRIC   INCANDESCENT  LIGHTING. 

in  weight  of  copper  throughout  the  supply 
conductors  of  a  three- wire  system  is  about 
67  1/2  per  cent,  over  that  necessary  for  a 
two-wire  system  having  the  same  loss  in 
transmission. 


A-f 


)   <§> 


c 
FIG.  56.— MULTIPLE-SERIES  CONNECTION. 

Fig.  56  represents  a  multiple-series  sys- 
tem equivalent  to  a  three-wire  system  with 
no  neutral,  and  supplied  at  230  volts  pres- 
sure. The  disadvantage  of  such  a  system, 
however,  is  that  two  lamps  have  to  be 
turned  on  and  off  simultaneously.  The 
three- wire  system  of  Fig.  55  gives  inde- 
pendent control  over  every  lamp. 


SYSTEMS   OF   LAMP  DISTRIBUTION.        225 

The  principle  of  the  three-wire  system 
has  been  extended  to  four-  and  five-wire 
systems.  Four-wire  systems  are  very  rare. 
Five-wire  systems  are  employed  in  Europe 
but  have  never  come  into  favor  in  the 
United  States.  A  five-wire  system  saves 
about  ninety  per  cent,  of  the  copper  re- 
quired for  a  two-wire  system,  but  requires 
four  dynamos  in  series  at  the  central  sta- 
tion, five  sets  of  conductors  and  complica- 
tion in  house  wiring  and  meters. 

The  three-wire  system  is  in  very 
extended  use  in  the  United  States.  It 
commonly  happens  that  one  three-wire 
central  station  will  distribute  light  and 
power  over  an  area  whose  radius  is  some- 
what greater  than  one  mile,  whereas,  with- 
out the  use  of  the  three- wire  system,  the 
radius  of  commercial  incandescent  lighting 
from  a  central  station  would  be  probably 


226      ELECTRIC   INCANDESCENT   LIGHTING. 

only  about  one-half  a  mile  or  eight  times 
less  area. 

The  drop  of  pressure,  which  is  permitted 
in  incandescent  lighting,  does  not  depend 
entirely  upon  the  activity  uselessly  ex- 
pended in  the  main  conductors.  For  ex- 
ample, in  cases  where  capital  would  be 
difficult  to  secure,  and  the  interest  upon 
the  capital  invested  would  be  large,  it 
would  be  desirable  to  employ  compara- 
tively small  conductors,  and  waste  a  com- 
paratively large  percentage  of  the  total 
power  in  them.  This  would  necessitate  a 
comparatively  great  difference  of  electric 
pressure  between  the  lamp  terminals  and 
the  generator  terminals.  In  the  case  of  a 
single  house  supplied  with  115-volt  lamps, 
it  would  not  be  a  matter  of  much  conse- 
quence whether  the  pressure  at  the  central 
station  were  116  or  166  volts,  provided 


SYSTEMS   OF  LAMP  DISTRIBUTION.        227 

the  lamp  pressure  remained  constant,  but 
where  incandescent  lamps  are  distributed 
along  street  mains,  in  a  city,  and  have 
to  be  supplied  at  all  distances  from  a  few 
yards  to  a  mile  or  more  from  the  central 
station,  it  is  absolutely  necessary  that  the 
pressure  shall  be  nearly  uniform  through- 
out the  system,  since,  otherwise,  the  lamps 
in  or  near  the  station  will  be  at  an 
unduly  high  pressure,  and  will  conse- 
quently *be  brilliant  and  short-lived,  while 
the  more  distant  lamps  will  be  burned  at 
an  unduly  low  pressure,  and  be  dull  and 
long-lived.  The  drop  of  pressure  permis- 
sible in  the  supply  conductors  is,  conse- 
quently, as  much  a  matter  of  regulation 
of  pressure,  and  of  uniformity  of  candle- 
power,  as  it  is  a  consideration  of  economy 
in  the  transmission  of  electric  power.  If 
lamps  were  less  sensitive  to  changes  in 
pressure  than  they  are,  the  amount  of  cop- 


228      ELECTRIC   INCANDESCENT   LIGHTING. 

per  which  would  be  employed  in  incan- 
descent lighting  would  be  less  than  it 
actually  is,  but  all  the  improvements  made 
of  recent  years  in  incandescent  lamps  have 
been  improvements  in  their  efficiency, 
whereby  a  smaller  amount  of  activity  is 
required  for  a  given  production  of  light, 
and  this,  as  we  have  seen,  is  attended  by 
the  development  of  a  higher  tempera- 
ture and  a  greater  sensibility  to  variations 
in  pressure,  so  that  the  most  economical 
lamps  are  also  lamps  which,  other  things 
being  equal,  require  a  closer  regulation  of 
pressure  at  their  terminals. 

The  difficulty  of  maintaining  a  nearly  uni- 
form pressure  over  all  parts  of  the  mains  of 
a  large  incandescent  system  has  been  largely 
overcome  by  the  use  of  what  are  called 
feeders.  A  feeder  differs  from  an  ordinaiy 
supply  conductor,  or  main,  in  that  no  lamp 


SYSTEMS   OF   LAMP   DISTRIBUTION.        229 

or  receptive  device  is  directly  connected 
with  it ;  its  sole  purpose  being  to  supply 
the  mains  from  the  central  station  at  some 
distant  point  as  indicated  in  Fig.  57. 
Here  D,  is  the  dynamo  at  the  central 
station.  F  F,  are  feeders  carrying  the 
current  from  the  dynamo  to  some  cen- 


J       ) 
— i — i 


F 

FIG.  57.—  FEEDER  DISTRIBUTION. 


tral  point  in  the  mains  A  Aly  B  B^ 
In  this  way  the  difference  in  pressure  be- 
tween the  various  lamps  depends  only 
on  the  drop  of  pressure  in  the  mains,  and 
not  on  the  drop  of  pressure  in  the  feeder. 
Thus,  if  the  pressure  at  the  lamps  at  A  and 
Al9  be  115  volts,  the  pressure  at  the  feed- 
ing point  F,  may  be  116  volts,  while  the 
pressure  at  the  dynamo  may  be  150  volts. 


230      ELECTRIC   INCANDESCENT   LIGHTING. 

If  the  same  lamps  were  supplied  without 
feeders  as  shown  in  Fig.  58,  and  the  same 
limiting  difference  of  pressure  maintained 
between  the  lamps  as  in  Fig.  57,  namely  1 
volt,  it  would  be  necessary  to  have  prac- 
tically 116  volts  at  the  dynamo  terminals 
and  115  volts  at  the  most  distant  lamp. 


B  • 

FIG.  58.— TREE  DISTRIBUTION. 

This  probably  would  require  much  more 
copper  in  supply  conductors  than  when 
feeders  are  employed.  The  conductors  in 
Fig.  58  are  shown  as  tapering  or  diminish- 
ing in  size  towards  the  distant  end. 

Feeders  may  equally  well  be  applied  to 
three-wire  systems.  Fig.  59  represents 
diagrammatically  the  supply-mains  of  a 
city  district  containing  four  blocks,  1,  2,  3 


SYSTEMS   OF   LAMP   DISTRIBUTION. 


231 


and  4.  Here  the  three- wire  mains  extend 
round  the  block-facings  in  one  continuous 
network.  These  mains  are  supplied  from 
the  central  station  at  S9  by  the  three- wire 


FIG.  59. — DIAGRAM  OP  THREE- WIRE  FEEDER 
DISTRIBUTION. 

feeders  represented  by  the  dotted  lines,  at 
the  feeding  points,  A,  B,  C  and  D.  In 
this  way  the  pressure  in  the  network  of 
mains  may  be  within  two  per  cent,  of  the 
mean  value,  of  say,  115  volts,  while  the 
pressure  at  the  central  station  may  be  130 
volts,  representing  a  drop  in  the  feeders  of 


232      ELECTRIC    INCANDESCENT    LIGHTING. 

15  volts.  If  the  lamps  were  connected 
across  the  feeders  they  would  be  subjected 
to  a  total  difference  of  pressure,  over  the 
entire  system,  amounting  to  17  volts,  but, 
by  connecting  the  lamps  to  the  mains  only, 
they  are  rendered  entirely  independent  of 
the  drop  which  occurs  in  the  feeders. 

If  the  system  of  mains  be  unequally 
loaded,  as  for  example,  when  the  area  over 
which  they  extend,  comprises  both  a  resi- 
dence district  and  a  business  district,  so 
that  the  load  shifts  in  the  morning  and 
afternoon  to  the  business  district,  and  in 
the  evening,  almost  entirely  to  the  resi- 
dence district,  it  may  happen  that  the 
load  on  some  particular  feeders  may  be 
much  greater  than  the  load  on  others. 
Consequently,  the  drop  in  the  loaded 
feeders  will  be  in  excess  of  that  on  the 
comparatively  idle  feeders.  Under  these 


SYSTEMS   OF   LAMP   DISTRIBUTION.        233 

circumstances,  the  pressure  at  the  mains, 
near  the  terminals  of  the  idle  feeders,  will 
be  higher  than  that  at  the  terminals  of  the 
loaded  feeders,  thus  bringing  about  an 
inequality  of  pressure,  prejudicial  to  the 
life  and  proper  performance  of  the  lamps. 

The  difficulty  arising  from  the  inequal- 
ity in  the  feeder  load  may  be  overcome  in 
one  or  more  of  four  ways  : 

(1)  By    disconnecting    certain     feeders 
from  the  bus-bars,  or  main  terminals  in  a 
central  station,  so  as  to  increase  the  load 
and  drop  on  the  remaining  feeders. 

(2)  By  introducing  artificial  resistances, 
called  feeder  regulators,  into  the  circuit  of 
the  idle  feeders;  so  as  to  increase  artificially 
the  drop  of  pressure  which  exists  in  them. 

(3)  By  employing  more  than  one  pres- 
sure in  the  central  station,  that  is  to  say, 
by  having  one  set  of  dynamos  operating  at 


234      ELECTRIC    INCANDESCENT   LIGHTING. 


FIG.  60. — FEEDER  EQUALIZER  RESISTANCE. 


LAMP   DISTRIBUT^W      235 

for  the 


a  pressure 

supply  of  the  shorter  feeders  to  tlie  area 
AN7ithin  the  vicinity,  and  another  set  of 
dynamos  delivering,  perhaps,  135  volts,  for 


FIG.  61.— EQUALIZER  SWITCH. 

the  supply  of  longer  feeders  connected  to 
the  outlying  districts. 

(4)  By  introducing   more   copper    into 
the  system,  either  in  the  form  of  additional 


236      ELECTRIC   INCANDESCENT   LIGHTING. 

feeders,  so  as  to  share  and  equalize  the 
load,  or  in  the  form  of  more  numerous 
mains  to  distribute  and  equalize  the  pres- 
sure. 

Fig.  60,  represents  a  form  of  resistance, 
suitable  for  feeder  regulation.  Here  a 
number  of  spirals  of  heavy  iron  wire  are 
mounted  in  a  fire-proof  frame  and  so 
arranged  that  under  the  influence  of  the 
handle  and  switch,  shown  in  Fig.  61,  they 
may  be  inserted  in  the  circuit  of  a  feeder 
either  in  parallel  or  miseries. 

In  modern  large  central  stations  feeder 
equalizers  are  rarely  employed.  The  best 
practice  employs  more  than  one  pressure. 


CHAPTER  XII. 

HOUSE   FIXTURES    AND    WIRING. 

THE  incandescent  lamp,  when  located  in 
a  house,  is  either  installed  as  a  fixture,  or  a 
certain  freedom  of  motion  is  given  to  it, 
so  that,  within  certain  limits,  the  lamp  is 
portable.  This  portability  is  effected  by 
maintaining  the  lamp  in  connection  with 
the  mains  by  means  of  a  flexible  conductor 
or  lamp  cord,  usually  called  a  flexible  cord. 
The  lamp  is  then  portable  to  the  extent 
of  the  length  of  the  cord.  Various  forms 
are  given  to  portable  lamps,  two  of  which 
are  shown  in  Figs.  62  and  63.  In  Fig.  62, 
the  flexible  cord  c  c,  is  attached  to  a  read- 
ing lamp,  mounted  on  a  stand  as  shown. 


238      ELECTRIC   INCANDESCENT   LIGHTING. 


FIG.  62. — PORTABLE  LAMP  FOII  DESK  USE. 

This    lamp    can    be    raised  and  lowered 
within  a  limited  range,  as  well  as  turned 


HOUSE   FIXTURES   AND   WIRING.         239 


FIG.  63. — FLEXIBLE  LAMP  PENDANT  WITH  ADJUSTER. 


240      ELECTRIC   INCANDESCENT   LIGHTING. 

about  its  axis  without  shifting  the  base. 
Fig.  63,  shows  a  form  of  movable  lamp,  in 
which  a  limited  portability  is  obtained  by 
what  is  generally  known  as  a  flexible 
pendant.  Here  the  lamp  is  hung  from 


FIG.  64. — FLEXIBLE  SUPPORT  FOB  LAMP. 

the  ceiling  by  a  flexible  lamp  cord.  By 
means  of  an  adjuster  J^  the  lamp  can  be 
raised  or  lowered. 

The  limited  portability  given  to  a  lamp, 
by   attaching    it    to    a    sufficiently    long 


HOUSE  FIXTURES   AND   WIRING.          241 

flexible  pendant,  enables  the  light  to  be 
applied  to  a  variety  of  purposes,  such,  for 
example,  as  the  lighting  of  a  music  stand, 


FIG.  65. — FLEXIBLE  SUPPORT  FOR  DESK  LAMP. 

as  shown  in  Fig.  64,  or  the  lighting  of  a 
desk,  as  shown  in  Fig.  65.  Fig.  66,  shows 
a  device  for  tilting  a  flexible  pendent  lamp 
in  any  desired  direction. 

Fixed  lamps,  as  their   name   indicates, 
are  lamps  attached  to  electric  fixtures,  and, 


242    ELECTRIC  INCANDESCENT  LIGHTING. 

therefore,  cannot  be  moved.  They  take  a 
great  variety  of  forms,  such  as  the  bracket 
lamp  shown  in  Fig.  67,  designed  for 


Jflfe 


FIG.  66.— TILTED  LAMP. 


For    ceiling 


attachment  to  the  wall, 
attachment,  lamps  are  either  made  of  the 
simple  pendant  type,  as  shown  in  Fig.  68, 
or  several  lamps  are  placed 


together 


HOUSE   FIXTURES   AND    WIRING.          243 

in  a  cluster  in  an  electrolier,  as  shown  in 
Fig.  69.  As  in  gas  lighting,  the  incandes- 
cent bracket  lamp  is  sometimes  given  a 
movable  arm  so  as  to  permit  the  lamp  to 


FIG.  67. — BRACKET  LAMP. 

be  moved  in  one  plane,  within  a  certain 
radius.     Such  a  lamp  is  shown  in  Fig  70. 

The  size  of  the  wire  employed  inside 
a  house  will  depend  upon  the  amount  of 
current  which  the  conductor  is  designed  to 


244     ELECTRIC  INCANDESCENT  LIGHTING. 


FIG.  68.— PENDANT  LAMP. 


HOUSE   FIXTURES   AND    WIRING. 


245 


carry.     When  of  small  size,  the  conductor 
is  given   the  form  of  a  single  wire,  but, 


FIG.  69.— ELECTROLIER. 


in  order  to  secure  greater  flexibility,  larger 
sizes   are  almost  invariably  stranded,  that 


246      ELECTRIC   INCANDESCENT   LIGHTING. 

is,  composed  of  several  independent  wires. 
The  former  are  called  solid  wires  and  the 
latter  stranded  wires.  In  Fig.  71,  the 
solid  conductor  is  marked  <?,  and  has  one 
coating  of  insulator  d,  which  is  afterward 


FIG.  70. — BRACKET  LAMP  WITH  MOVABLE  ARM. 

covered  by  a  braiding  b.  The  stranded 
conductor  shown  at  C\  consists  of  seven 
wires,  twisted  together  as  shown,  and  is 
covered  by  two  coatings  of  insulating 
material,  I)  and  E,  respectively,  and 
finally  by  a  coating  of  braid  B. 

Fig.     72,    shows    two    other    forms    of 
stranded  conductors ;  the  wire  marked  A, 


HOUSE  FIXTURES   AND    WIRING. 


247 


is  provided  with  a  highly  insulating 
material  called  okonite ;  that  marked  B, 
has  in  addition,  a  coating  of  braid.  The 
wire  at  A,  is  equivalent  to  No.  6  A.W.  Gr. 


d  b 

FIG.  71. — SOLID  AND  STRANDED  CONDUCTORS. 

in  cross-sectional  area.  The  insulation  re- 
sistance of  a  mile  of  this  wire,  when  sub- 
merged in  water,  is  1,000  million  ohms, 
that  is,  one  billion  ohms,  or  a  begohm. 

A  flexible  cord,  such  as  has  already 
been  referred  to  in  connection  with  port- 
able lamps,  is  necessarily  a  double  con- 


248      ELECTRIC    INCANDESCENT   LIGHTING. 

due  tor,  since  the  current  must  be  passed 
both  into  and  out  of  the  lamp.  These 
two  conductors  are  separately  insulated, 
and  are  then  either  twisted  together,  form- 
ing what  is  called  a  twisted  double  con- 


FIG.  72.— OKONITE-COVERED  STRANDED  WIRES. 

ductor,  or  are  laid  side  by  side,  and  laced 
together  by  a  covering  of  braid,  forming 
what  are  then  called  parallel  or  twin  con- 
ductors. Fig.  73,  shows  some  forms  of 
double  flexible  conductors.  These  are 
first  separately  insulated  and  are  then  silk- 
covered.  They  are  sometimes  technically 
called  silk  lamp  cord.  In  order  to  attain 


HOUSE   FIXTURES    AND   WIRING.          249 

the  flexibility  required  in  such  cords  they 
are  composed  of  a  comparatively  large 
number  of  fine  copper  wires  stranded  to- 
gether. 


FIG.  73. — FORMS  OF  DOUBLE  FLEXIBLE  CONDUCTORS. 

We  will  now  trace  the  network  of  con- 
ductors in  a  house  which  we  will  suppose 
receives  its  current  from  the  street 
mains,  to  the  lamps  in  the  different  por- 
tions of  the  house.  First;  proceeding 
from  the  street  to  the  house,  we  find  a  set 
of  conductors  leading  into  the  house, 


250      ELECTRIC    INCANDESCENT   LIGHTING. 

called  the  service  wires.  These  in  a  two- 
wire  system  consist  of  two  conductors,  and 
in  a  three-wire  system  of  three  conductors. 
Within  the  house  the  system  of  conduct- 
ors may  be  arranged  under  the  following 
heads;  namely, 

(1)  The    risers,    or    the    supply    wires 
which  carry  the  current  up  from  the  ser- 
vice wires   to   the   different  floors   of   the 
house.     They  may  be   a    single  set   or   a 
multiple  set,  but  each  set  will  be  double 
or  triple  according  as  the  house  is  wired 
on  the  two-  or  three-wire  system. 

(2)  The  mairts,  or  the  principal  supply 
conductors  running  from  the  risers  or  ser- 
vice wires  along  the  different  corridors  or 
passages.     There  are  usually  as  many  sep- 
arate systems  of  mains  as  there  are  floors. 

(3)  The   sub-mains   or    the   supply-con- 
ductors which  branch  off  from  the  mains 
along  the  side  passages. 


(4)  jBT§$&$®t  fft.jfffl^  qpj|$fed^m>m  the 
mains  into  i^T^uuIiIi?"uT  **to  fixtures  in 
halls.  Roughly  speaking,  therefore,  the 
risers  correspond  to  the  trunk  of  a  tree 
through  which  the  sap  is  fed ;  the  mains 
correspond  to  the  boughs  ;  the  sub-mains 
to  the  smaller  boughs ;  and  the  branches 
to  the  twigs.  The  lamps  or  fixtures  cor- 
respond to  the  leaves  and  flowers. 

Risers  are  usually  of  larger  cross-section 
than  the  mains;  the  mains  are  of  larger 
cross-section  than  the  sub-mains,  and  the 
sub-mains,  in  their  turn,  are  larger  than 
the  branches.  This  must  naturally  be  the 
case,  since  the  risers  must  carry  all  the 
current,  the  mains  divide  the  current 
among  themselves,  and  the  branches  carry 
only  the  current  of  the  few  lamps  wired 
upon  them.  We  may  imagine  that  each 
lamp  has  a  certain  size  of  wire  connected 


252      ELECTRIC   INCANDESCENT   LIGHTING. 

with  it  from  the  street  mains,  direct  to  the 
socket,  and,  that  since  these  wires  run  side 
by  side,  they  may  be  regarded  as  collected 
into  a  single  larger  wire,  such  as  a  main  or 
riser. 

The  smallest  size  of  wire  which  is  per- 
mitted to  be  used  in  wiring  a  building, 
in  the  United  States,  is  No.  18  A.  W.  G. 
wire,  having  a  diameter  of  0.040". 

The  wiring  of  a  building  should  be  de- 
signed in  such  a  manner,  that  when  all  the 
lamps  are  burning  at  any  one  time,  the  drop 
in  pressure  between  the  street  mains  and  the 
most  distant  lamp  shall  not  exceed  a  cer- 
tain small  percentage,  usually  three  per 
cent.  This  drop  is  calculated  by  deter- 
mining the  total  amount  of  current  in 
amperes  which  will  pass  through  the  vari- 
ous mains,  sub-mains  and  branches,  deter- 


HOUSE  FIXTURES   AND   WIRING.          253 

mining  for  each  such  a  resistance  as  will, 
when  carrying  this  current,  produce  drops 
of  pressure,  the  maximum  sum  of  which 
along  any  line  shall  not  exceed  the  re- 
quired percentage. 

In  very  large  buildings,  a  feeder  system  is 
sometimes  employed ;  that  is  to  say,  the 
service  wares  are  connected  by  feeders 
to  centres  of  distribution,  from  which 
mains  extend  both  upward  and  down- 
ward. 

Two  supply  wires,  carrying  the  full  lamp 
pressure  between  them,  are  never  per- 
mitted to  remain  in  contact  with  each 
other,  even  though  both  are  insulated, 
except  in  cases  of  flexible  conductors, 
which  are  in  plain  view  and  which  never 
carry,  under  normal  circumstances,  a  pow- 
erful current. 


254      ELECTRIC   INCANDESCENT  LIGHTING. 

Insulated  wires  are  never  allowed  to 
come  into  contact  with  concealed  wood- 
work, but  when  passing  through  wooden 
beams  or  floors  should  be  protected  by  in- 
sulating tubes  of  porcelain  or  hard  rubber. 

There  are  three  methods  of  carrying 
out  interior  wiring;  namely, 

(1)  Cleat  work. 

(2)  Moulded  work. 

(3)  Concealed  work. 

Cleat  work  is  the  simplest  and  cheapest, 
but  least  ornamental  type  of  wiring.  The 
wires  are  carried  in  insulating  receptacles, 
of  wood  or  porcelain,  in  plain  view  on  the 
ceilings  or  upper  part  of  the  walls.  The 
wires  should  never  rest  directly  upon  the 
walls  or  ceilings,  but  should  be  supported 
by  the  cleat,  a  full  half  inch  away  from 
the  same. 


HOUSE   FIXTURES   AND   WIRING.          255 

Fig.  74,   shows   two   forms   of   wooden 
cleats.     Fj   f]  are  the  front  pieces  which 


FIG.  74. — WOODEN  CLEATS. 


clamp  the  wires,  and  B  B,  are  the  brackets 
which   support   the    wires   free   from    the 


256      ELECTRIC    INCANDESCENT   LIGHTING. 

walls.  S  Sj  are  the  screw  holes  by  which 
the  cleats  are  secured  in  place  and  clamped 
together.  The  wires  of  opposite  polarity 
are  always  separated  by  such  cleats  to  a 


FIG.  75. — FORM  OF  SCREW  CLEAT. 

distance  at  least  2  1/2"  apart.  Cleat  work 
is  only  suitable  for  indoor  work  in  dry 
localities.  Figs.  75  and  76  show  forms  of 
screw  cleats  employing  respectively  wood 
and  glass  insulation  around  the  wire. 


HOUSE   FIXTURES   AND   WIRING. 


257 


Moulded  work  is  more  expensive  than 
cleat  work,  but  presents  a  more  sightly  ap- 
pearance. Fig.  77,  shows  different  forms  of 
three-wire  moulding,  suitable  for  different 


FIG.  76. — FORM  OF  SCREW  CLEAT. 

sizes  of  conductor.  The  moulding  is  made 
in  two  parts ;  namely,  the  base  or  mould, 
with  the  grooves  formed  in  it,  and  the 
upper  part,  or  capping,  which  covers  the 
mould.  These  moulds  and  cappings  are 


258      ELECTRIC   INCANDESCENT   LIGHTING. 

usually  made  of  soft  pine,  and  are  cut  into 
lengths  of  about  ten  feet.     The  moulds  are 


FIG.   77. — SECTIONS  OF  MOULDINGS. 

first  screwed  in  position  on  the  walls  or 
ceilings ;  the  wires  are  then  laid  in  them, 
and,  finally,  the  cappings  are  secured  by 


HOUSE   FIXTURES   AND   WIRING. 


259 


screws  over  them,  care  being  taken  not  to 
injure  the  conductors  in  screwing  on  the 
cappings.  The  mouldings  are  usually 


FIG.  78. — PICTURE  AND  ORNAMENTAL  MOULDING. 

painted  of  a  color  to  conform  with  the 
ornamentation  of  the  walls  or  ceilings  on 
which  they  rest.  Fig.  78,  represents  at  Py 


260      ELECTRIC   INCANDESCENT   LIGHTING. 

a  form  of  moulding  suitable  for  hanging 
pictures  around  the  walls  of  a  room,  and 
at  0,  a  type  of  ornamental  moulding. 

The  most  difficult  problem  connected 
with  the  distribution  of  wires  by  moulding, 
lies  in  the  connection  of  the  electroliers 
with  the  wires  in  the  passages  without 
presenting  an  unsightly  appearance.  This 
is  sometimes  accomplished  by  the  use  of 
dummy  moulding,  or  ornamental  mouldings 
symmetrically  arranged  on  the  ceiling  from 
the  centres  of  the  electrolier,  in  one  only  of 
which  mouldings  the  wires  are  placed. 

The  best  solution  of  the  problem  of 
avoiding  the  unsightly  appearance  of  wires 
is  obtained  by  concealed  work,  where  the 
conductors  are  buried  under  floors  or  in  the 
walls  and  ceilings.  This  method  should 
not  be  adopted  unless  the  wires  besides 


HOUSE   FIXTURES    AND    WIRING.          261 

their  insulating  cover,  are  provided    with 
a  moisture-proof  sheet  or  tube  of  papier- 


FIG.  79. — INTERIOR  CONDUITS. 

mache   or   metal.     Such   protecting  tubes 
form  in  reality  a  conduit  employed  inside 


262      ELECTRIC    INCANDESCENT   LIGHTING. 

the     building    and    generally    called     an 
interior   conduit. 


Interior  conduits  may  be  made  in  a 
variety  of  ways,  one  of  which  is  shown 
in  Fig.  79.  Conduits  made  of  tubes  of 
papier-mache  are  soaked  in  a  bituminous 


m 


FIG.  80.— BRASS-COVERED  CONDUIT. 

solution,  which  serves  the  double  purpose 
of  rendering  them  insulating  and  practi- 
cally water-proof.  Moreover,  when  house 
wires  are  carried  through  a  complete 
system  of  interior  conduits,  the  wires  can 
be  withdrawn  and  replaced  at  any  time 
without  disturbing  the  walls  or  ceilings. 
Fig.  80,  shows  a  conduit  tube  sheathed 
with  a  thin  layer  of  brass  so  as  to  be 


HOUSE   FIXTURES   AND   WIRING. 


263 


water-tight.  Fig.  81,  shows  a  brass  tube 
joint  connecting  different  lengths  of  con- 
duit. Aj  is  a  joint  for  connecting  ordinary 
conduit,  and  B,  a  joint  connecting  brass- 
covered  sheathed  conduit.  Where  several 


FIG.  81.— INTERIOR  CONDUIT  JOINTS. 

conduits  are  united  together,  a  junction  box 
is  provided  containing  a  number  of  outlets, 
corresponding  with  the  number  of  conduits 
as  shown  in  Fig.  82.  These  boxes  are 
closed  by  a  metallic  cover.  Fig.  83,  shows 
two  forms  of  connecting  boxes  for  holding 


264      ELECTRIC    INCANDESCENT   LIGHTING. 

joints  between  the  mains  and  branches  of  a 
two- wire  or  three-wire  system  running  in 


FIG.  82. — INTERIOR  CONDUIT  JUNCTION  BOXES. 

interior  conduits.  The  branch  wires  in 
this  case  proceed  from  the  box  through 
the  smaller  apertures.  In  cellars  the  con- 


HOUSE   FIXTURES   AND    WIRING. 


265 


duits  are  frequently  heavily  sheathed  with 
brass  or  iron. 


FIG.  83. — CONNECTION  Box  FOH  INTERIOR  CONDUITS. 

The  cost  of  wiring  a  building  depends 
in  a  great   measure  upon   the  number  of 


266      ELECTRIC    INCANDESCENT   LIGHTING. 

outlets  required,  that  is  on  the  number 
of  points  at  which  the  wires  must  be 
brought  out  for  connection  to  switches  and 
lamps.  Where  the  lamps  are  installed  in 
groups,  as  in  electroliers,  fewer  outlets  are 
required  and  the  cost  is  less  than  if  the 
lamps  were  installed  singly. 

Concealed  work  is  generally  much  more 
readily  and  cheaply  installed  during  the 
construction  of  a  building  than  at  a  sub- 
sequent period.  It  has  become  customary 
in  large  cities  to  wire  all  new  buildings, 
even  though  no  arrangement  has  been 
made  to  supply  them  immediately  with 
electric  current.  In  some  cases  interior 
conduits  are  placed  in  a  new  building  with 
the  intention  of  subsequently  wiring  the 
building. 

It  is  often  convenient  to  be  able  to  turn 


G.        267 

some  dis- 
(Ts  purpose,  be- 
sides the  key  frequently  provided  in  the 
socket  for  turning  on  or  oft*  the  individual 
lamp,  lamp-switches  are  placed  in  the 
branches,  or  in  the  mains,  whereby  all  the 
lamps  supplied  by  said  branches  or  mains 
may  be  lighted  or  extinguished  at  once. 
The  size  and  character  of  the  lamp  switch 
will  depend  upon  the  current  strength  it 
is  intended  to  control.  Switches  may  be 
divided  into  two  general  classes ;  namely, 
single-pole  switches  and  double-pole  switches. 
In  a  single-pole  switch,  as  the  name  indi- 
cates, the  connection  is  broken  on  one  side 
only  of  the  two  supply  conductors;  in  a 
double-pole  switch,  it  is  broken  on  both 
sides.  Switches  are  made  in  a  great 
variety  of  forms,  a  few  of  which  are  illus- 
trated in  the  accompanying  figures.  Fig. 
84,  shows  a  form  of  simple  single-pole 


268      ELECTRIC    INCANDESCENT   LIGHTING. 

switch.  By  turning  the  key  K,  the  spring 
/SY,  is  brought  into  contact  with  the  supply 
spring  P,  thereby  ensuring  the  closing  of 
the  branch  circuit  of  the  lamp  through  the 


FIG.  84.— SIMPLE  FORM  OP  SINGLE-POLE  SWITCH. 

switch  terminals  A  and  B.  Single-pole 
switches  should  never  be  employed,  except 
for  a  small  number  of  lamps.  Fig.  85, 
shows  a  different  type  of  switch.  $,  being 
a  single-pole  switch,  with  two  terminals, 
and  Dj  a  double-pole  switch  with  four. 


HOUSE  FIXTURES  AND   WIKING.         269 

s 


FIG.  85.— SINGLE-  AND  DOUBLE-POLE  SWITCHES. 

In  the  latter  case,  two  of  these  terminals 
are  connected  with  the  branch  wires  and 
the  other  two  with  the  supply  mains. 


270      ELECTRIC   INCANDESCENT   LIGHTING. 

Fig.  86,  shows  a  larger  form  of  double-pole 
switch,  intended  for  a  comparatively  large 
number  of  lamps,  say  100.  Generally,  care 


FIG.  86. — LARGER  FORM  OF  DOUBLE -POLE  SWITCH. 

is  given  to  make  the  contacts  of  considera- 
ble surface  area,  in  order  that  no  undue 
heating  may  arise  from  imperfect  contact. 
Fig.  87,  represents  a  different  type  of 


HOUSE  FIXTURES   AlSTD    WIRING. 


PIG.  87. — DOUBLE-POLE  SWITCH. 


272      ELECTRIC   INCANDESCENT   LIGHTING. 

double-pole  switch.  Here  the  turniDg  of 
the  handle  forces  a  lever  into  or  out  of  a 
groove,  whereby  the  contact  pieces,  A  B 
and  CD,  are  either  insulated  or  are  con- 
nected together. 

Fig.  88,  represents  a  form  of  switch 
which  is  sunk  into  the  wall,  so  that  its 
plane  outer  surface  is  flush  with  the  sur- 
face of  the  wall.  The  switch  is,  therefore, 
usually  called  a  flush  switch. 

In  normal  operation,  the  current  which 
passes  through  the  conductors  in  a  build- 
ing is  only  that  which  is  necessary  to  sup- 
ply the  high  resistance  lamps  connected 
with  them.  If,  however,  an  accidental 
short-circuit,  or  direct  connection,  were  to 
take  place  between  the  positive  and  nega- 
tive mains  in  any  part  of  the  building,  the 
supply  wires  connected  with  those  mains 


HOUSE   FIXTURES   AND   WIRING.          273 

would  be  apt  to  receive  a  rush  of  current 
that  might  render  them  white  hot.  In 
order  to  prevent  the  danger  arising  from 
this  overheating,  a  form  of  automatic 


FIG.  88. — FLUSH  SWITCH. 

switch  has  been  designed,  which  im- 
mediately opens  the  overloaded  circuit, 
and  thus  interrupts  the  current.  The 
automatic  switch  invariably  employed  in 
incandescent  mains  is  quite  simple  in  its 
construction  and  operation.  It  is  called 


274      ELECTRIC   INCANDESCENT   LIGHTING. 

a  fuse  cut-out,  or  safety  fuse,  and  consists 
essentially  of  a  strip  or  wire  of  lead,  or 
fusible  alloy,  interposed  in  the  circuit. 
The  area  of  cross-section  of  the  fuse  strip 
is  such  that,  while  it  will  readily  carry  the 
normal  current  intended  to  be  supplied  by 
the  conductors  with  which  it  is  connected, 
it  will  immediately  fuse  on  the  passage  of 
an  abnormal  current. 

Fig.  89,  shows  a  form  of  branch  cut-out; 
i.  e.,  a  fuse  block  inserted  between  a  pair 
of  branch  wires  and  the  mains  supplying 
them.  These  branch  Hocks  consist  of  a 
glazed  porcelain  base,  provided  with  two 
grooves  in  which  are  four  terminals  A,  B, 
O  and  Dj  one  pair  of  which,  say  A  and  B, 
are  connected  to  the  branch  wires,  while 
the  other  pair,  O  and  D,  are  connected  to 
the  mains.  A,  is  connected  to  6y,  and  B, 
to  Z>,  through  two  strips  /SJ  S9  of  fusible 


FIXTURES  AND  WIRING.       275 

alloy,  clamped  at  the  ends  under  smaller 
screws,  as  shown.      A  suitable   porcelain 


FIG.  89.— BRANCH  BLOCK. 


cover  is  screwed  over  the  whole,  so  that 
the  fuse  is  completely  protected.  If  the 
current  passing  into  the  branch  wires  be- 


276      ELECTRIC   INCANDESCENT   LIGHTING. 

comes  dangerously  strong,  the  fuses  S,  S9 
are  melted  or  blown,  and  thus  automatically 
interrupt  the  branch  circuit. 

Various  forms  of  fuses  are  employed. 
A  common  type  is  represented  in  Fig.  90. 
Here  the  fuse  consists  of  lead-alloy  wire 
inserted  in  a  small  glass  plug  P,  somewhat 
resembling  the  socket  of  a  lamp.  This 
plug  screws  into  receptacles  in  the  cut-out, 
in  such  a  manner  that  when  a  fuse  is 
melted  or  blown,  it  is  only  necessary  to 
remove  the  plug  and  screw  in  a  new  one. 
The  forms  of  cut-out  shown  are  designed 
for  use  in  connection  with  two-wire  or 
three-wire  mains. 

A  complete  system  of  house  wiring 
includes  a  number  of  fuses.  Large  fuses 
are  inserted  in  the  service  wires,  where 
they  enter  the  cellar,  these  being  usually 


HOUSE   FIXTURES   AND    WIRING.         277 


FIG.  90.— PLUG  CUT-OUTS. 


called  the  main  fuses.  The  main  cut-out 
fuses  are  usually  placed  close  to  a  main- 
switch,  where  the  current  can  be  turned 


278      ELECTKIC    INCANDESCENT   LIGHTING. 

on  or  off  from  the  house  at  will.  All  con- 
nections between  risers  and  mains,  or 
between  mains  and  -sub-mains,  or  sub-mains 
and  branches,  are  usually  provided  with 
fuse  cut-outs  of  the  size  corresponding  to 
the  current  which  they  have  to  carry.  In 
the  circuits  of  the  various  fixtures  small 
fuses  are  frequently  inserted.  Fig.  91, 
represents  a  few  types  of  such  fixture  cut- 
outs, as  they  are  called,  shaped  to  conform 
with  the  fixtures  for  which  they  are 
intended.  If  a  short  circuit  should  take 
place,  close  to  an  individual  lamp,  the 
small  fuses  in  the  lamp  circuit  would  melt, 
either  at  the  fixture  cut-out,  or  at  the 
branch  cut-out  supplying  the  same.  If  a 
short  circuit  take  place  in  a  sub-main,  the 
fuse  at  the  junction  between  the  main  and 
sub-main  would  likewise  melt,  while 
finally,  if  a  short  circuit  should  occur  in 
one  of  the  larger  mains,  the  fuses  in  the 


PRCPERTY  CF      i 


CHOUSE   FIXTURES   AND 


279 


FIG.  91. — FIXTURE  CUT-OUTS. 

main  cut-out,  where  the  service  wires  enter 
the  building,  would,  probably,  be  instantly 
blown. 


In  all  large  installations,  it  is  important 


280      ELECTRIC    INCANDESCENT   LIGHTING. 

to  be  able  to  detect  quickly  the  location  of 
a  melted  fuse   in    order  that   it    may   be 


FIG.  92.—  DISTRIBUTION  Box. 

replaced     and     tlie    extinguished    lamps 
restored  as  soon  as  possible.     This  is  fre- 


HOUSE   FIXTURES   AND    WIRING. 


281 


quently  done  by  collecting  all  the  fuses 
belonging  to  some  particular  portion  of 
the  system  at  a  point  called  a  distributing 


FIG.  92A. — DISTRIBUTION  Box. 

point,  usually  at  a  junction  of  risers  and 
mains,  or  mains  and  sub-mains.  The  in- 
take wires  ;  i.  e.,  those  which  feed  the  box, 
are  usually  brought  to  a  pair  of  metal  bars 


282      ELECTRIC   INCANDESCENT   LIGHTING. 

in  a  box  called  a  distribution  box  lined 
with  some  fire-proof  material  let  into  the 
wall.  The  out-put  wires;  i.  e.,  those  which 
take  their  supply  from  the  box,  are  at- 
tached to  separate  terminals  which  main- 
tain connection  with  the  metal  strips, 
through  safety  fuses  of  the  proper  size. 

Figs.  92  and  9  2 A,  illustrate  a  particular 
form  of  distribution  box,  which  is  let  flush 
into  the  wall  and  lined  with  fire-proof  mate- 
rial. A  B,  are  the  two  intake  wires.  This 
box  is  intended  for  use  in  connection  with  a 
two- wire  system.  A,  is  placed  in  electric 
connection  with  the  metal  strip  g  li,  and  B, 
with  the  metal  strip  &  Z,  through  two  safety 
fuses.  The  out-put  wires  are  a  b,  c  d  and 
ef;  a,  c  and  e,  being  positive  and  b,  d  and/, 
negative.  These  wires  are  all  placed  in  elec- 
tric connection  with  their  respective  strips, 
each  being  provided  with  a  safety  fuse,  as 


HOUSE   FIXTURES    AND    WIRING.          283 

shown,  s,  s,  s,  are  three  switches,  for  con- 
trolling their  independent  circuits.  Fig. 
92 A  shows  the  box  with  its  cover  in  posi- 
tion, but  with  the  door  opened.  At  the 
top  of  Fig.  92  is  a  cross-section  of  the  box. 
In  many  cases  these  boxes  have  glass  doors 
through  which  the  condition  of  the  fuses 
can  be  readily  inspected. 


CHAPTER  XIII. 

STREET    MAINS. 

IN  small  towns,  systems  of  incandescent 
distribution  are  effected  by  means  of  over- 
head wires  or  overhead  main  conductors; 
that  is  to  say,  both  feeders  and  mains  are 
insulated  wires  supported  on  poles.  This 
method  of  construction  is  adopted,  both  on 
the  score  of  economy  and  the  ease  of  inspect- 
ing, repairing  and  connecting  the  Avires. 
In  large  cities,  however,  where  the  number 
of  such  conductors  is  necessarily  greatly 
increased,  and  where,  moreover,  multi- 
tudinous conductors  are  required  for  other 
than  electric-lighting  systems,  the  wires 
are,  to  a  greater  or  less  degree,  necessarily 
buried  underground. 


STREET   MAINS.  285 

Three  methods  are  applicable  to  under- 
ground conductors ;  namely,  subways,  con- 
duits and  tubes.  Of  these  methods,  the  first 
two  provide  means  whereby  the  wires  can 
be  replaced  or  removed  with  greater  or  less 
readiness.  By  the  third  method,  the  tubes 
are  actually  buried  in  the  ground  and  need 
excavation  for  examination  or  repair. 

A  subway  differs  from  a  conduit,  in  that 
it  consists  of  an  underground  tunnel  of 
sufficient  dimensions  to  permit  the  passage 
of  a  man.  Underground  subways,  unques- 
tionably provide  the  readiest  means  for 
operating  an  extended  system  of  con- 
ductors. There  are,  however,  two  serious 
difficulties  that  lie  in  the  way  of  their 
extensive  adoption  ;  namely,  expense,  and 
want  of  room.  In  our  larger  cities,  an 
unfortunate  lack  of  uniformity  has  existed 
in  the  mode  of  use  of  the  space  beneath 


286      ELECTRIC   INCANDESCENT   LIGHTING. 

the  streets,  and  pavements,  for  the  location 
of  the  sewer,  gas  and  water-pipes,  steam 
heating  pipes,  and  the  various  systems  of 
electric  conductors  which  are  to-day  so 
imperatively  needed  in  a  modern  city. 
Unfortunately,  in  too  many  cases,  the 
location  of  these  lias  been  placed  under 
the  control  of  different  and  frequently 
antagonistic  officials.  A  lack  of  space  has 
consequently  resulted,  so  that  in  most  of 
our  large  cities,  the  construction  of  a  sub- 
way system  would  require  an  entire  recon- 
struction of  the  systems  of  sewers,  water, 
gas  and  electric  mains. 

Where  a  subway  is  employed,  it  is 
necessary  to  ensure  its  complete  drainage 
and  also  to  provide  for  an  efficient  system 
of  ventilation,  whereby  the  accidental 
leakage  of  gas  into  the  subway  shall  not 
produce  explosive  mixtures  with  air. 


STREET   MAINS.  287 

The  conduit  affords  a  much  readier  and 
more  easily  applied  system  for  under- 
ground mains  or  conductors.  A  conduit 
differs  from  the  subway  in  that  it  merely 
provides  a  space  for  the  wire  or  cable. 
Various  forms  of  conduits  have  been 
devised,  but  all  consist  essentially  of 
means  whereby  tubes,  intended  for  the 
reception  of  cables,  and  generally  of  some 
insulating;  material,  are  buried  in  the 

o  / 

ground.  They  are  provided  with  man- 
holes, or  a  free  space  in  the  street,  extend- 
ing below  the  level  of  the  conduits, 
large  enough  to  admit  a  workman. 
When  it  is  desired  to  introduce  a  wire 
into  a  conduit,  or  to  replace  an  injured 
wire,  the  wires  are  drawn  into  or  from 
the  conduits  at  the  manholes. 

Figs.  93  and  94,  illustrate  in  section  a 
conduit  formed  of  creosoted  wood,  laid 


288    ELECTRIC  INCANDESCENT  LIGHTING. 

together  in  sections,  so  as  to  leave  cylin- 
drical spaces  between  them,  through 
which  the  wires  or  cables  may  be  drawn. 
This  system  is  frequently  used  for  the 


FIG.  93. — CONDUIT  OP  CREOSOTED  WOOD. 

reception     of     lead-covered      high-tension 
wires,    and   telephone   cables. 

While  overhead  conductors  may  be  un- 
objectionable in  small  towns  or  villages, 
yet,  in  large  cities,  where  the  need  for 
wires  is  great  and,  moreover,  is  con- 


STREET   MAINS.  289 

stantly  increasing,  a  condition  of  affairs 
might  readily  be  brought  about  such  as 
is  shown  in  Fig.  95,  which  represents 
the  condition  of  a  street  with  the 


FIG.  94. — CONDUIT  OF  CREOSOTED  WOOD  CUT  AWAY  TO 
SHOW  STRUCTURE. 


many  aerial  wires  that  are  to  be  ex- 
pected. Contrast  this  with  the  altered 
appearance  of  the  same  street,  when  the 
wires  were  placed  in  underground  con- 
duits as  shown  in  Fig.  96,  and  the  advan- 
tage of  underground  wires,  from  an  aesthetic 
standpoint,  is  manifest. 


290      ELECTRIC   INCANDESCENT   LIGHTING. 


FIG.  95. — VIEW  OP  CITY  STREET  WITH  OVERHEAD  WIRES. 


STREET  MAINS.  291 


FIG.   96. — VIEW  OF  CITY   STREET   AFTER  REMOVAL  OF 
OVERHEAD  WIRES. 


292      ELECTRIC   INCANDESCENT   LIGHTING. 

Fig.  97,  represents  the  third  method  for 
underground  conductors,  viz.;  the  under- 
ground tube.  Here  an  iron  pipe  is  em- 
ployed, containing  three  insulated  conduc- 
tors, and  intended  for  use  in  a  three- wire 

J 


FIG.   97.— TUBE  CONTAINING  THREE  SEPARATELY 
INSULATED  CONDUCTORS. 

system  of  distribution.  The  iron  pipe  is 
provided  for  the  purpose  of  protecting  the 
conductors  from  mechanical  injury.  Fig. 
98,  shows  cross-sections  of  different  sizes 
of  these  tubes.  A,  B  and  C,  are  the  cross- 
sections  of  the  copper  conductors,  sur- 
rounded and  supported  by  a  bituminous 
insulating  material.  The  outer  ring  is  the 
section  of  the  iron  pipe. 

As  the  above  form  of  underground  tube 
is  to-day  in  extended  use,  a  description  of 


STREET   MAINS.  293 

its  manufacture  will  not  be  out  of  place. 
The  iron  pipes  are  made  up  in  lengths  of 
twenty  feet.  The  copper  conductors,  cut 
off  to  the  right  length,  are  prepared  for 


FIG.   98.— MAIN  TUBES. 

placing  in  the  tube  by  wrapping  each 
with  a  loose  or  open  spiral  of  rope. 
Three  rods  are  then  assembled  and  held 
together,  in  the  position  shown  in  the 
cross-section,  by  wrapping  them  with  a 
tight  wrapping  of  rope.  The  rods  so 
assembled,  are  now  placed  in  a  length  of 
tube,  and  one  end  of  the  tube  is  closed 


294      ELECTRIC   INCANDESCENT   LIGHTING. 

with  a  plug.  The  tube  is  then  filled 
with  hot  bituminous  insulating  material. 
The  tube  is  finally  closed  by  a  second 
block.  There  will  thus  be  provided, 


FIG.  99. — SECTION  OP  STREET  TRENCH  CONTAINING  A 
FEEDER  AND  MAIN  TUBE. 

lengths  of  pipe  twenty  feet  long,  con- 
taining three  insulated  conductors  with 
their  extremities  projecting  at  the  ends. 

The  underground  tubes  so  formed  are 


£//     295 

V5>    h 

Y-    // 

sent  dBJbCftoni  the  factory  inc  me r '  twenty - 

T^>!    4*'  ff?v-r~M^  'r 

foot   sectionfeteseril)ed.     They  are  subse- 

«/ 

quently  connected  to  one  another,  while 
in  position  in  the  underground  trench 
prepared  to  receive  them.  Fig.  99,  shows 
a  section  through  a  trench  provided  for 
a  feeder  and  a  main  tube.  The  trench 
is  usually  30"  deep,  as  shown,  and  is 
situated  in  the  street  a  short  distance 
from  the  curb,  the  pipes  being  laid  end  to 
end  at  the  bottom  of  the  trench. 


It  now  remains  to  connect  the  separate 
lengths  of  the  underground  tubes.  For 
this  purpose  coupling  boxes  are  provided 
as  shown  in  Fig.  100.  A,  shows  a  coup- 
ling box  suitable  for  a  street  connection, 
and  B,  a  coupling  box  for  a  right-angled 
connection.  The  coupling  box  is  formed 
of  a  cast  iron  shell  made  in  halves, 
connected  together  by  bolts  passing 


296      ELECTRIC    INCANDESCENT    LIGHTING. 

through  flanges,  and  clamped  over  collars 
secured  at   the   ends  of   the  tubes.     The 


FIG.   100. — COUPLING  BOXES. 

collars  are  first  secured  in  place.  The 
lower  half  of  the  box  is  then  fitted  and 
the  three  flexible  copper  stranded  con- 


STREET   MAINS.  297 

nectors  are  forced  on  the  ends  of  the  con- 
ductors as  shown.  By  the  aid  of  a  torch, 
the  joints  are  all  heated  to  a  sufficiently 
high  temperature,  and  solder  is  melted 
into  them,  thus  forming  a  good  metallic 
junction.  The  upper  half  of  the  box  is 
then  fitted  into  place,  the  two  parts 
clamped  together  by  the  bolts,  and  melted 
bituminous  compound  is  poured  into  the 
box  through  an  aperture  in  the  top.  The 
coupling  box  is  then  closed  as  shown  at  J 
in  Fig.  97. 

Fig.  101,  shows  a  form  of  branch  coup- 
ling box  suitable  for  a  house-service  con- 
nection with  the  mains.  In  this  case,  A. 
and  B,  are  main  tubes  passing  along  the 
street,  while  C\  is  the  house  service  tube. 
Here  the  coupling  box  is  shaped  to  con- 
form to  the  requirements  of  the  triple 
connection  as  shown. 


298      ELECTRIC    INCANDESCENT   LIGHTING. 

Fig.  102,  shows  cross-sections  of  feeder 
tubes.  In  these  tubes,  the  neutral  con- 
ductors are  of  smaller  size  than  the  two 
outside  conductors,  since  the  system  is 


FIG.  101.— BRANCH  COUPLING  Box. 

arranged  to  be  nearly  balanced  as  to  load 
with  reference  to  the  neutral.  The  three 
small  black  wires  shown,  are  called  pressure 
wires;  i.  e.,  small  insulated  copper  con- 
ductors which  are  returned  from  the  feed- 
ing point,  or  point  of  junction  between 


STREET  MAINS.  299 

feeder  and  mains,  to  the  central  station,  so 
as  to  indicate  in  the  central  station,  the 
pressure  which  is  supplied  to  the  mains. 
Thus,  if  the  drop  in  the  feeders,  be  say  15 


FIG.   102.— FEEDER  TUBES. 

volts,  and  the  pressure  at  the  bus-bars,  in 
the  central  station,  be  130  volts  on  each 
side  of  the  system,  or  260  volts  across  out- 
side bus-bars,  the  pressure  in  the  mains  at 
the  feeding  point  will  be  115  volts  on  each 
side,  and  this  will  be  the  pressure  carried 
by  the  small  pressure  wires  back  to  the 
indicators  at  the  central  station. 


300      ELECTRIC    INCANDESCENT   LIGHTING. 


FIG.  103. — JUNCTION  Box. 


Fig.  103,  shows  the  interior  and  Fig.  104, 
the  exterior  of  a  junction  box  ;  i.  e.,  a  box 
situated  at  the  junction  of  two  streets,  or 


STREET  MAINS.  301 

at  a  feeding  point  where  a  feeder  joins  the 
mains.  This  box  is  of  cast  iron,  and  is 
buried  with  its  surface  flush  with  the 
street  level.  The  tubes  enter  the  sides  of 


FIG.  104. — JUNCTION  Box. 

the  box  at  the  lower  level.  The  conduct- 
ors are  connected  by  flexible  connections 
with  brass  pieces  supported  on  insulating 
rings.  These  pieces  are  marked  +  and  - 
according  to  the  polarity  of  the  conductors 
connected  with  them. 


302     ELECTRIC   INCANDESCENT  LIGHTING. 

Three  metallic  rings,  insulated  from  eacli 
other,  are  provided  in  the  box  corresponding 
to  the  three  conductors  in  the  tubes.  All 
the  positive  conductors  are  connected  across 
to  the  positive  ring,  through  fuse  strips ;  all 
the  negative  conductors  are  connected  to 
the  negative  ring ;  and  all  the  neutral  con- 
ductors, to  the  neutral  ring.  In  this  way  all 
the  positive  conductors  are  placed  in  elec- 
trical connection  with  each  other,  and  also 
the  negative  and  neutral  conductors.  The 
box  is  made  water-tight  by  lowering  a 
cover  over  the  bolts  seen  in  the  ring  in  the 
upper  part,  screwing  down  nuts  upon 
these  bolts,  and  pouring  in  bituminous 
compound  in  a  melted  state  over  the  bolts. 
J?,  is  a  feeder  tube  containing  the  pressure 
wires  and  five  conductors,  a  pair  of  nega- 
tives, a  pair  of  positives,  and  a  neutral. 
MM,  are  main  tubes ;  p,  is  a  slab  or  strip 
of  insulating  material,  supporting  the  con- 


STREET  MAINS. 

nections  for  the  pressure  wires,  which  are 
connected  through  fuses  with  the  three 
rings  in  the  box.  Fig.  104,  shows  the 
appearance  of  the  junction  box  when  closed 
with  an  ornamental  cover. 


CHAPTER  XIV. 

CENTRAL    STATIONS. 

IF  we  could  follow  the  buried  conduct- 
ors through  the  streets,  up-stream,  that  is, 
toward  the  supply,  we  would  finally  reach 
a  building  toward  which  all  these  wires 
converge.  This  building  constitutes  what 
is  called  a  central  station.  In  it  we  will 
find  the  means  for  generating  the  current 
which  is  sent  through  the  street  mains  and 
feeder  wires,  through  the  service  conduct- 
ors into  the  house,  and  finally  through  the 
risers  and  house  mains  and  branches,  to 
the  lamps.  Limiting  our  description  of 
the  station  to  one  in  which  continuous 
electric  currents  only  are  generated;  i.  e., 


304 


CENTRAL   STATIONS.  305 

currents  which  always  flow  in  the  same 
direction,  and  which  are  suitable  for  use  in 
the  three-wire  system  of  buried  conductors 
just  described,  and  supposing,  as  is  gener- 
ally the  case,  that  steam  power  is  employed, 
we  will  find  that  the  apparatus  can  be 
readily  grouped  into  three  general  classes  ; 
namely, 

(1)  The  dynamos. 

(2)  The  engines. 
(a)  The  boilers. 

Directing  our  attention  in  the  station 
first"  to  that  part  of  the  building  at  which 
the  feeders  enter  from  the  street,  we  will 
find  them  connected  to  a  device  called  a 
switchboard.  This  consists  essentially  of  a 
fire-proof  frame  supporting  a  number  of 
metallic  terminals  provided  for  connection 
with  the  feeders  and  also  with  connections 
designed  to  receive  conductors  from  the 


306      ELECTRIC   INCANDESCENT  LIGHTING. 

generators.  A  number  of  instruments  are 
mounted  on  this  switchboard,  consisting  of 
ammeters  to  show  the  strength  of  current, 
and  voltmeters  to  show  the  pressure  on  the 
various  feeders,  while  switches  are  pro- 
vided for  opening  and  closing  the  various 
circuits. 

Fig.  105,  shows  a  partial  view  of  a 
switchboard  in  a  central  station.  /SJ  /S7,  S, 
are  rows  of  massive  switches  mounted 
upon  fire-proof  slabs  of  insulating  material. 
Above  the  switches  are  the  voltmeters  and 
ammeters,  while  at  F,  are  the  field  regulat- 
ing boxes  for  controlling  the  pressure  of 
the  generators.  During  the  daytime,  the 
load  on  the  mains  is  principally  due  to 
motors  arid  is  considerably  less  than  the 
night  load.  As  evening  approaches,  the 
load  increases,  as  is  shown  on  the  ammeters 
at  the  station.  As  soon  as  it  becomes 


PRCFCRTY  OF 


308      ELECTRIC   INCANDESCENT   LIGHTING. 

necessary  to  introduce  another  pair  of 
dynamos,  the  engine  driving  them  is 
started,  the  pressure  of  the  dynamos  is 
brought  up  to  that  required,  and  the 
switches  are  then  closed  at  the  switch- 
board, thus  connecting  the  new  generators 
with  the  feeders.  The  reverse  process  is 
adopted  as  the  load  diminishes,  and  it  is 
unnecessary  to  any  longer  maintain  the 
extra  generators  in  the  circuit. 

Fig.  106,  shows  a  type  of  generator  unit 
frequently  met  with  in  large  central 
stations,  for  low-pressure  incandescent-light 
distribution.  This  figure  represents  a  por- 
tion of  the  engine  room  in  a  large  central 
lighting  station,  and  shows  two  generator 
units  at  A  and  B,  respectively.  A,  is  a 
vertical  condensing,  triple-expansion  engine, 
Ej  E,  E,  whose  main  horizontal  shaft 
drives  at  each  end  the  armature  of  a  dy- 


310      ELECTRIC   INCANDESCENT   LIGHTING. 

namo  or  generator  6r,  to  be  presently 
described.  This  engine  has  two  platforms 
P,  P.  This  engine  runs  at  120  revolu- 
tions per  minute,  developing  a  maximum 
of  800  HP;  or,  approximately,  600  KW, 
the  two  generators  being  of  200  KW 
capacity  each.  At  B,  is  a  smaller  generat- 
ing unit  of  similar  construction,  provided 
with  a  single  platform  />,  and.  also  driving 
two  smaller  dynamo  armatures,  each  of  100 
KW  capacity,  the  maximum  out-put  of  the 
engine  being  300  KW,  or  about  400  HP, 
at  172  revolutions  per  minute. 

It  is  evident,  under  these  circumstances, 
that  when  the  engine  is  developing  its  full 
load,  the  dynamos  will  be  overloaded  about 
forty  per  cent.  Owing  to  the  fact  that 
the  full  load  on  a  central  station  is  of  short 
duration,  this  has  been  found  to  be  an 
economical  practice. 


CENTKAL   STATIONS.  311 

In  order  to  provide  power  to  drive  the 
engines  and  dynamos  a  battery  of  boilers 
is  installed.  Boilers  are  of  various  types. 
Since  an  incandescent  lamp  requires  an 

activity  of  50  watts,  or  about  tpth  of  one 

horse-power  at  its  terminals,  and  since 
losses  occur  in  the  feeders,  mains  and 
house  wires  of,  perhaps,  ten  per  cent,  on 
an  average,  the  activity  per  lamp  at  the 
dynamo  terminals,  in  a  central  station,  will 
be  about  55.5  watts.  Moreover,  since  an 
average  loss  of  say  fourteen  per  cent, 
occurs  in  the  engine  and  dynamo,  the 
activity  per  lamp,  generated  by  the  engine, 
must  be  about  64.5  watts,  or  about  the 

T—^th  of  a  horse-power,  so  that  on  an  aver- 

1  l.D 

age,  one  indicated  horse-power  at  the 
engine,  represents  11.5  sixteen-candle  power 
incandescent  lamps  of  50  watts  each.  In 


312      ELECTRIC   INCANDESCENT   LIGHTING. 

other  words,  the  average  commercial  effi- 
ciency of  such  a  system  of  distribution, 
starting  from  the  indicated  horse-power 
of  the  engine,  is,  approximately,  77.5  per 
cent.  About  17  pounds  of  steam,  at  160 
pounds  pressure,  are  required  per  indicated 
horse-power-hour  with  engines  of  the  type 
shown.  This  represents  about  2.9  pounds 
of  coal  per  horse-power-hour  delivered 
electrically  in  consumers'  lamps. 

A  large  central  station  may  readily  sup- 
ply 60,000  incandescent  lamps  or  more. 
Assuming  that  60,000  is  supplied  at  maxi- 
mum load,  the  boiler  power  needed  will  be 
correspondingly  great.  Take,  for  example, 
the  central  station  that  was  required  to 
supply  the  buildings  and  grounds  of  the 
World's  Columbian  Exhibition  at  Chicago, 
in  1893,  with  electric  light.  There  were 
employed  for  lighting  this  exhibition, 


CENTRAL   STATIONS.  313 

about  100,000  incandescent  lamps  and 
about  5,000  arc  lamps.  There  was 
naturally  required  for  this  purpose,  as 
well  as  for  driving  the  machinery  in  the 
buildings,  a  very  great  amount  of  power. 

Fisf.   107,  shows    a  view  of   the    main 

O  ' 

boiler  plant  in  the  above  exhibition.  Here 
batteries  of  boilers,  representing  an  aggre- 
gate of  24,000  horse-power  are  shown. 
_/),  Z>,  are  the  main  doors,  d,  d,  the  fire 
doors,  and  beneath  these  latter  the  ash-pit 
doors.  6r,  is  the  steam  gauge  to  show  the 
steam  pressure  in  the  boiler  above  that  of 
the  atmosphere ;  g,  the  water  gauge ;  M,  the 
steam  drum,  and  P,  the  main  steam  pipe. 

To  the  student  of  the  incandescent 
lamp,  the  most  important  features  of  the 
central  station  are  the  dynamos  or  genera- 
tors designed  to  supply  the  current  to  the 


314      ELECTRIC   INCANDESCENT   LIGHTING. 

lamps.  Limiting  our  attention  now  to 
continuous-current  dynamos,  we  will  find 
these  to  be  of  a  variety  of  types,  although  all 
operate  on  essentially  the  same  principle. 

Broadly  speaking  a  dynamo-electric  ma- 
chine or  generator,  is  a  device  whereby 
electromotive  forces,  and  from  these,  elec- 
tric currents  are  produced,  generally  by 
the  revolution  of  conductors  through 
magnetic  flux.  The  magnetic  flux  is  pro- 
duced by  field-magnet  coils.  E.  M.  Fs.  are 
set  up  in  the  coils  on  the  revolving  por- 
tion, called  the  armature.  These  E.  M. 
Fs.  are  generated  in  the  armature  coils 
in  successively  opposite  directions,  as  they 
pass  each  pole ;  consequently,  they  need 
to  be  commuted,  or  caused  to  assume  the 
same  direction  in  the  external  circuit. 
This  is  effected  by  a  device  called  a  com- 
mutator. 


316      ELECTRIC    INCANDESCENT   LIGHTING. 

Thus  Fig.  106,  represents  muJMpolar 
generators,  there  being  fourteen  magnets  or 
poles  Jt/J  Mj  My  on  the  large  dynamo,  and 
eight  magnets  or  poles,  on  the  small  dynamo. 
These  magnets  form  part  of  the  massive 
stationary  iron  frames  F  F  F,f  f  f,  sup- 
porting the  outboard  bearings  O,  o.  In 
the  cylindrical  bore  of  these  field-magnet 
poles,  run  the  armatures,  which  are  rigidly 
secured  to  the  main  engine  shaft.  A  light 
metallic  frame  supports  a  number  of  pairs 
of  brushes  B,  B,  upon  the  surface  of  the 
commutator,  there  being  as  many  pairs  of 
brushes  as  poles,  so  that  A,  has  fourteen 
pairs  of  brushes  upon  its  commutator  and  B, 
has  eight  pairs.  These  pairs  of  brushes,  or 
double  brushes,  as  they  might  be  called,  are 
insulated  from  their  supporting  frame,  but 
are  connected  in  alternate  pairs  with  the 
main  terminals  T,  T.  Thus  the  first,  third, 
fifth,  etc.,  brushes  are  connected  to  one 


CENTRAL   STATIONS.  317 

terminal,  and  the  second,  fourth,  sixth,  etc., 
with  the  other.  H,  h,  are  handles  for  rock- 
ing the  entire  brush-holder  frame  to-and- 
fro  within  a  small  angular  range  around 
the  axis,  so  as  to  cany  all  the  brushes  for- 
ward or  backward  upon  the  surface  of  the 
commutator.  This  adjustment  is  made 
to  prevent  sparking  at  the  brushes  from 
the  current  which  they  carry  at  different 
loads.  The  main  terminals  T,  T,  are  con- 
nected to  switches  on  the  main  switch- 
board of  the  station. 

Fig.  108,  shows  in  greater  detail  another 
form  of  central  station  generator  of  the 
same  type.  F,  F,  F,  is  the  field  frame. 
M,  M,  My  are  the  field  fcoils,  six  in  num- 
ber, consisting  of  coils  of  insulated  wire 
wound  upon  soft  steel  cores  bolted  radially 
to  the  field  frame,  as  shown.  A.,  is  the 
armature  whose  surface  runs  within  the 


318      ELECTRIC   INCANDESCENT   LIGHTING. 

cylindrical  polar  space  formed  by  the  poles 
of  the  field  magnets.     (7,  C,  is  a  commu- 


FIG.  108. — SIX-POLE  GENERATOR. 

tator,  consisting  of  copper  strips,  rigidly  se- 
cured in  a  cylindrical  frame,  and  insulated 


from  one  anotl;fc«:^^ 
conducting  loops  wound  upon  the  arma- 
ture. 13,  It,  are  the  brushes,  of  which  there 
are  six  pairs,  connected  to  two  metallic 
rings,  one  ring  being  in  connection  with 
three  alternate  pairs.  These  rings  are 
finally  connected  to  the  main  terminals  T, 
Tj  by  cables,  as  shown.  The  current  sup- 
plied by  the  armature  is  collected  by  each 
brush,  leaving  the  armature  at  the  three 
positive  brushes,  and,  after  traversing  the 
external  circuit  of  the  feeders,  mains, 
house  wires  and  lamps,  returning  to  the 
armature  through  the  three  negative 
brushes,  thereby  completing  the  electric 
circuit.  H,  is  a  handle  for  advancing  or 
retreating  the  brushes  over  the  surface  of 
the  commutator.  The  machine  shown  has 
50  KW  capacity,  that  is  to  say,  it  will 
deliver  at  its  terminals  activity  to  the 
amount  of  50  KW,  (400  amperes  at  a 


320      ELECTRIC   INCANDESCENT   LIGHTING. 

pressure  of  125  volts,  or  400  X  125  = 
50,000  watts).  It  requires  about  75 
horse-power  or  about  56  KW  to  drive  it 
at  full  load.  Its  gross  weight  is  6,500 
pounds,  representing  an  output  of,  approxi- 
mately, 7.7  watts  per  pound  of  total 
weight.  It  has  a  shaft  five  inches  in  di- 
ameter, and  occupies  a  space  of  30"  X  61" 
X  51"  in  height. 

The  armature  of  the  preceding  machine 
is  illustrated  in  greater  detail  in  Fig.  109. 
It  consists  of  a  metal  cylinder,  which  car- 
ries on  its  outer  surface  a  laminated  iron 
core,  built  up  of  annular  sheet-iron  discs, 
clamped  side  by  side,  so  as  to  form,  when 
assembled,  an  almost  complete  cylindrical 
external  surface  of  iron,  A  A.  Gaps  are 
left,  at  suitable  intervals  between  adjacent 
sets  of  discs,  to  provide  for  the  ventila- 
tion of  the  armature,  by  means  of  the  pas- 


CENTRAL   STATIONS. 


321 


sage  of  air  by  centrifugal  force  from  within 
outward,  to  aid  in  the  cooling  of  the  ar- 


FIG.  109. — ARMATURE  OF  GENERATOR. 

mature,   when   operated.     The   outer   sur- 
faces of  the  iron  discs  are  provided  with 


322      ELECTRIC   INCANDESCENT   LIGHTING. 

longitudinal  slots,  parallel  to  the  axis  of 
rotation.  These  slots  are  designed  to  re- 
ceive the  armature  conductors.  One  hun- 
dred and  sixty-eight  of  these  slots  are  thus 
provided  to  receive  one  hundred  and  sixty- 
eight  sets  of  conductors. 

The  winding  adopted  in  the  armature  is 
conducted  as  follows :  At  A,  a  pair  of 
rods  or  wires  comes  through  a  slot  across 
the  armature  surface.  A  pair  of  flexible 
copper  strips,  insulated  from  their  neigh- 
bors, are  soldered  to  the  rods  at  #,  and  run 
down  to  b.  These  connect  two  adjacent 
commutator  bars  at  b.  From  this  they  run 
back  behind  the  connections  W,  IF,  to  the 
slot  at  c,  and  then  across  the  armature  sur- 
face underneath  the  two  rods  or  wires 
which  are  seen  to  approach  at  c.  Having 
reached  the  opposite  side  of  the  armature 
at  c'y  they  descend  obliquely  on  the  other 


CENTRAL  STATIONS.  323 

face  to  a  point  opposite  d,  and  then  ascend 
to  the  armature  surface  at  a  point  c.  Here 
the  rods  connected  therewith  return  across 
the  armature  surface  to  the  point  0,  de- 
scending again  to  the  commutator  at  the 
point  f.  In  this  manner  a  pair  of  con- 
ductors zig-zag  across  the  armature,  via 
g  i  ~k,  emerging  again  one  slot  in  advance 
of  a,  and  so  on.  In  this  manner  it  must 
always  happen  that  the  wires  in  the  slot 
a,  pass  under  one  pole,  the  wires  c  e  g  i  Jc 
will  also  be  passing  under  the  other  poles. 
The  effect  of  the  commutator  is  to  enable 
the  brushes  to  collect  'all  the  currents 
which  are  being  generated  in  the  various 
wires  passing  under  the  different  poles  and 
to  unite  them  in  the  external  circuit. 


CHAPTER  XV. 

ISOLATED    PLANTS. 

FOR  the  general  purposes  of  house  light- 
ing, where  comparatively  few  lamps  are  re- 
quired, it  is  more  economical  for  the  house- 
holder to  rent  his  electric  power  from  a 
central  station,  than  it  would  be  for  him  to 
erect  and  maintain  his  own  plant.  Since 
a  plant  requires  boilers  and  engines,  it 
would  follow,  unless  a  fairly  considerable 
number  of  lamps  is  required,  that  the 
extra  expense  of  the  installation  as  well  as 
the  services  of  an  engineer,  or  engineer 
and  fireman,  would  make  it  much  cheaper 
in  such  cases  to  take  the  service  from  the 
street  mains  as  supplied  by  the  nearest 


ISOLATED   PLANTS.  325 

central  station.  There  are  many  cases, 
however,  in  which  either  the  number  of 
lights,  or  the  circumstances  are  such,  as  to 
warrant,  in  point  of  economy,  the  main- 
tenance of  what  may  be  called  an  isolated 
lighting  plant,  in  contradistinction  to  a 
central-station  lighting  plant. 

It  is  clear  that  when  the  number  of 
lights  required  reaches  a  certain  limit,  it 
may  be  preferable  to  maintain  an  isolated 
plant,  rather  than  to  rent  the  light,  since 
a  large  building  or  plant  would  thus 
possess  the  advantage  of  being  indepen- 
dent of  the  running  of  the  central  station, 
or  of  accidents  which  might  occur  to  the 
street  mains.  Moreover,  a  large  isolated 
plant,  being  necessarily  circumscribed  in 
the  area  of  its  distribution,  would  require 
a  much  smaller  outlay  or  expenditure  in 
copper,  and,  consequently,  may  be  built  to 


326      ELECTRIC   INCANDESCENT  LIGHTING. 

produce     light    cheaper    thaii    a     central 
station. 

But  even  in  cases  where  the  number  of 
lights  is  not  very  great,  circumstances  may 
arise  where  it  would  still  be  economical  to 
establish  an  isolated  plant.  Such  cases 
would  be  found,  for  example,  in  manufac- 
turing establishments,  where  boilers  and 
steam  engines  have  necessarily  to  be  main- 
tained in  action  during  the  time  that  light 
is  required.  Again,  isolated  plants  arc 
necessary  in  sections  of  country  remote 
from  central  stations.  A  brief  description 
of  isolated  plants  for  the  supply  of  in- 
candescent lighting  will,  therefore,  be  of 
interest. 

Any  suitable  form  of  dynamo  can  be 
used  for  an  isolated  plant.  The  dynamo 
may  be  driven  either  directly  from  the 
engine  shaft  or  by  means  of  leltimj.  The 


ISOLATED   PLANTS. 


327 


direct  connection  requires  less  floor  space, 
is  somewhat  more  efficient,  and  saves  wear 


FIG.  110. — BELT-DRIVEN  GENERATOR  FOR  ISOLATED 
PLANTS. 


330      ELECTRIC   INCANDESCENT   LIGHTING. 

of  belting,  but  possesses  the  disadvantage 
of  requiring  the  engine  to  run  at  a  com- 
paratively high  speed,  and  the  dynamo  at 
a  comparatively  low  speed.  This  means 
that  for  all  sizes  of  generator  below  50  KW 
at  least,  the  cost  of  a  direct-driven  plant 
is  greater  than  that  of  a  belt-driven  plant, 
because  a  slow-speed  dynamo  means  a 
heavier  and,  consequently,  a  more  expen- 
sive dynamo,  and  a  high-speed  engine  is 
more  difficult  to  maintain  in  running 
order. 

Fig.  110,  represents  a  bipolar,  or  two- 
pole,  generator,  driven  by  a  belt  from  a 
small  vertical  engine  with  its  governor 
inside  the  fly  wheel. 

Fig.  Ill,  represents  a  quadripolar  or 
four-pole  direct-driven  generator,  suitable 
for  isolated  plants.  In  this  case  the  en- 


332      ELECTRIC   INCANDESCENT  LIGHTING. 

gine  is  completely  enclosed  in  a  cast-iron 
shell  and  runs  in  oil. 

Fig.  112,  represents  a  type  of  isolated 
lighting  plant  employed  on  board  ships  and 
supplied  to  several  vessels  in  the  United 
States  Navy.  This  quadripolar  generator 
delivers  200  amperes  at  80  volts  pressure, 
or  16  KW,  at  a  speed  of  400  revolutions  per 
minute.  It  is  directly  connected  as  shown 
to  the  vertical  marine  engine. 

Fig.  113,  represents  an  isolated  three- 
wire  plant,  consisting  of  a  100-horse-power 
horizontal  steam  engine,  driving  two  32 
KW  quadripolar  generators  at  a  speed  of 
270  revolutions  per  minute.  The  magnet 
poles  in  this  case  are  inside  the  armature 
and  the  outer  surface  of  the  armature  has 
its  insulated  conductors  bare,  so  as  to  form 
a  commutator,  upon  which  the  sets  of 


ISOLATED  PLANTS. 


333 


brushes  shown  in  the  figure  can  rest. 
The  switchboard  for  controlling  the  vari- 
ous circuits  is  represented  behind  the 
machine  on  the  right  hand  side  of  the 
figure.  The  apparatus  required  for  such  a 
switchboard  is  similar  in  kind  to  that  of 
a  central  station,  but  usually  is  smaller  and 
less  complex. 


CHAPTER  XVI. 

METEES. 

THE  sale  of  any  product  requires  some 
suitable  unit  of  measure.  Since  electric 
power  is  undoubtedly  a  product  requiring, 
as  it  does,  the  establishment  of  an  expensive 
plant  for  its  production,  a  unit  of  measure 
is  necessary,  as  well  as  an  apparatus 
w^hereby  the  number  of  units  delivered  to 
the  customer  by  the  producer  may  be 
measured. 

Various  plans  have  been  devised  for  the 
measurement  of  electric  supply.  Of  these, 
however,  only  two  forms  are  in  general 
use  for  the  measurement  of  continuous-cur- 

334 


METERS.  335 

rent  supply.  One  of  these  forms  meas- 
ures the  quantity  of  electricity  delivered 
to  the  consumer  in  units  of  supply  called 
ampere-hours,  while  the  other  measures  the 
energy  in  watt-hours.  Each  of  these  forms 
of  apparatus  is  called  a  meter. 

Fig.  114,  shows  a  form  of  electrolytic 
meter  indicating  the  supply  in  ampere- 
hours.  This  apparatus  depends  for  its 
operation  on  the  fact  that  an  electric  cur- 
rent, when  sent  through  a  solution  of  zinc 
sulphate,  will  effect  a  decomposition  of  the 
solution,  depositing  metallic  zinc  on  a  zinc 
plate  connected  with  the  negative  termi- 
nal, and  dissolving  or  removing  an  equal 
quantity  of  zinc,  from  a  plate  of  zinc  con- 
nected with  the  positive  terminal.  The 
indications  of  this  meter  are  obtained  by 
carefully  weighing  the  plates,  before  and 
after  the  supply  they  are  to  measure  has 


336      ELECTRIC   INCANDESCENT   LIGHTING. 

passed  through  them.  After  the  meter 
has  been  in  use  for  some  time,  it  will  be 
found  that  the  zinc  plate  connected  to  the 
positive  terminal  has  decreased  in  weight, 


FIG.  114. — ELECTROLYTIC  METER. 

and  that  connected  with  the  negative 
terminal  has  increased  in  weight.  This 
difference  of  weight  is  a  measure  of  the 
number  of  ampere-hours  that  have  passed 
through  the  cell. 


METEES.  337 

In  the  interior  of  the  meter  box,  in  the 
upper  part,  are  two  large  strips  of  ger- 
man  silver  7t,  J?,  carrying  the  current  to 
be  supplied  to  the  lamps,  and  offering  a 
definite  small  resistance  to  its  passage. 
The  positive  and  negative  supply  wires 
enter  the  box  at  P  and  N,  and  are  se- 
cured to  the  terminals  P  and  N,  inside. 
As  the  meter  shown  is  a  three-wire  meter, 
it  consists  of  two  meters,  in  one  box,  one 
being  for  the  supply  on  the  positive  main, 
and  the  other  for  the  supply  on  the  nega- 
tive main.  If  the  number  of  lamps 
lighted  in  a  house,  on  each  side  of  the 
system,  were  always  the  same,  the  records 
of  these  two  meters  would  be  equal. 
When  the  current  passes  through  the  re- 
sistance J5  .7?,  it  establishes  a  certain  drop 
of  pressure,  as  already  explained  in  Chap- 
ter III.  This  drop  amounts  to  about  0.4 
volt  at  full  load.  In  a  pair  of  derived  or 


338      ELECTRIC   INCANDESCENT   LIGHTING. 

shunt  circuits,  connected  across  the  ex- 
tremities, of  each  strip  of  resistance  R,  is 
placed  a  pair  of  small  glass  bottles  with 
resistances  wound  on  a  spool  s,  behind 
them.  The  total  resistance  of  the  bottle, 
or  plating  bath,  and  the  spool  in  its  circuit, 
bears  such  a  relation  to  the  resistance  of 
the  shunt  R,  that  each  milligramme  of  zinc 
electroplated  on  the  surface  of  the  nega- 
tive zinc  plate  2,  represents  a  definite 
number  of  ampere-hours  of  current  sup- 
plied through  the  meter  according  to  its 
size.  The  plates  2,  2,  are  made  of  zinc  and 
mercury  alloy,  and  are  separated  from 
each  other  by  hard  rubber  washers. 
Copper  rods  extend  upwards  from  these 
plates  through  the  corks  <?,  <?,  to  the 
copper  clips  p,  p.  There  are  two  bottles 
for  each  side  of  the  meter,  so  that  a  dupli- 
cate record  is  kept  on  each  side  of  the 
supply.  It  is  usual  to  renew  the  bottles 


METERS.  339 

once  a  month.  The  bottles  after  being  re- 
moved are  emptied,  the  zinc  plates  washed 
and  dried,  and  weighed  in  a  chemical  bal- 
ance, and  the  amount  of  the  supply  deter- 
mined from  the  difference  in  weight  dur- 
ing the  month.  The  solution  employed  is 
of  pure  zinc  sulphate  in  water,  having  a 
density  of  1.11  at  60°  F.  The  advantage 
of  this  meter  is  its  simplicity,  and  the  fact 
that  all  its  essential  working  parts  are  re- 
moved and  replaced  once  a  month.  The 
disadvantage  of  the  meter,  is  that  it  does 
not  show  directly  to  the  consumer,  the 
amount  of  supply  which  has  been  de- 
livered. 

When  such  meters  are  placed  in  ex- 
posed situations,  where  the  solutions  might 
be  liable  to  freeze,  a  thermostat  is  em- 
ployed to  maintain  the  temperature  of  the 
bottles  above  the  freezing  point.  Such  a 


340      ELECTRIC   INCANDESCENT   LIGHTING. 

thermostat  is  shown  in  Fig.  115.  Here  a 
metallic  strip,  composed  of  two  unequally 
expansible  metals  riveted  together,  is  so 
arranged,  that,  when  exposed  to  a  suffi- 

p 


FIG.  115. — THERMOSTAT  FOR  ELECTROLYTIC  METERS. 

ciently  low  temperature,  the  unequal  con- 
traction of  the  metals  will  cause  a  bending 
or  warping,  which  will  close  the  circuit  of 
a  lamp  through  the  set  screw  s.  The 
lamp  will  then  burn  until  the  temperature 
rises  sufficiently  to  allow  the  strip  p  p,  to 
straighten  and  break  the  circuit. 


METEKS. 


341 


Another  form  of  meter  in  general  use  is 
shown  in  Fig.  116.  In  this  form  of  in- 
strument, the  number  of  watt-hours  deliv- 
ered to  the  consumer  is  registered.  It 


FIG.  116.—  INTERIOR  OF  RECORDING  WATTMETER. 


342      ELECTEIC   INCANDESCENT   LIGHTING. 

consists  of  a  small  motor,  the  field  magnet 
coils  M,  M,  of  which  are  in  the  direct  cir- 
cuit of  supply.  The  armature  A,  placed 
within  the  field  coils,  revolves  upon  the 
vertical  shaft  S9  8,  with  a  speed  propor- 
tional to  the  activity  delivered ;  i.  e.,  to  the 
product  of  the  volts  and  amperes.  For 
example,  if  the  pressure  at  the  house 
mains  be  110  volts,  and  the  current  be  2 
amperes,  then  the  activity  delivered  would 
be  110  X  2  =  220  watts;  and,  in  one  hour, 
this  rate  of  delivery  would  result  in  a 
supply  of  220  watt-hours,  while  the  rotary 
speed  of  the  armature  shaft  would  be  pro- 
portional to  this  value  220.  A  small  com- 
mutator is  seen  just  above  the  field  coils 
with  its  long  slender  brushes  running 
back  to  supports  behind  the  apparatus. 
The  armature  is  placed  in  a  circuit  of  high 
resistance  across  the  mains,  so  that  it  ab- 
sorbs a  constant  small  amount  of  activity, 


METERS. 


343 


FIG.  117. — RECORDING  WATTMETER. 

whether  the  meter  be  running  or  not. 
The  shaft  engages  by  means  of  an  endless 
screw  with  a  pinion  wheel,  forming  part 


344      ELECTRIC    INCANDESCENT   LIGHTING. 

of  a  train  work  of  dial-recording  median- 

o 

ism,  similar, to  that  of  a  gas  meter. 

The  above  form  of  the  apparatus,  when 
completely  enclosed,  is  seen  in  Fig.  117. 
The  cover  is  secured  to  the  base  by  a  wire 
sealed  with  the  leaden  seal  s.  The  supply 
and  output  wires  pass  through  the  meter 
beneath.  The  advantage  of  this  meter  is 
that  it  enables  the  customer  to  observe 
the  amount  of  power  he  consumes.  Its 
disadvantage  is  that  it  constantly  absorbs 
a  small  amount  of  power.  A  meter  should 
always  be  installed  in  a  dry  place,  and 
inserted  in  the  service  wires  between  the 
street  main  cut-out  and  the  risers. 


CHAPTER  XVII. 

STORAGE    BATTERIES. 

IF  the  supply  of  electric  current  re- 
quired for  incandescent  lamps  was  uni- 
form throughout  the  twenty-four  hours,  it 
would  be  easy  to  determine  the  most  eco- 
nomical generator  units  of  boiler,  engine 
and  dynamo,  in  order  to  meet  this  require- 
ment economically.  Unfortunately,  how- 
ever, in  nearly  all  cases  the  variations  in  the 
load  are  very  great.  A  few  hours  of  the 
twenty -four  require  a  load  greatly  in  excess 
of  the  average.  If,  in  order  to  meet  this 
load  economically,  the  generating  plant  be 
subdivided  into  a  number  of  small  units, 
so  as  to  permit  them  to  be  readily  with- 
drawn and  added  as  required,  both  the 


345 


346      ELECTRIC   INCANDESCENT   LIGHTING. 

expense  arid  the  complexity  of  the  gener- 
ating system  would  be  necessarily  in- 
creased. If,  on  the  other  hand,  a  large 
generating  unit  be  installed,  it  would 
have  to  be  operated  for  the  greater  part  of 
the  twenty-four  hours  at  a  very  small 
load,  and,  therefore,  uneconomically. 

The  above  difficulty  is  sometimes  met 
by  the  employment  of  storage  batteries, 
which  are  charged  during  the  hours 
of  light  load,  and  discharged  during  the 
hours  of  heavy  load,  thereby  equalizing 
the  load  on  the  station.  Since,  at  the 
time  of  full  load,  the  output  is  obtained 
both  from  dynamos  and  storage  batteries, 
it  is  evident  that  a  much  smaller  generat- 
ing plant  of  boilers,  engines  and  dynamos 
is  rendered  necessary. 

In  order  to  determine  whether  it  would 


STORAGE   BATTERIES. 


347 


be  economical  to  install  a  storage  battery, 
it  is  necessary  to  ascertain  the  load  diagram 
of  the  station ;  that  is,  the  curve  which  rep- 
resents the  output  required  to  supply  the 


FIG.  118.— LOAD  DIAGRAM. 


lamps  during  the  twenty-four  hours  of  the 
day.  Such  a  load  diagram  is  shown  in  Fig. 
118.  In  this  figure  the  hours  of  the  day  are 
marked  off  horizontally,  and  the  current 


348      ELECTRIC   INCANDESCENT   LIGHTING. 

strength  delivered  to  the  feeders  is 
marked  off  vertically  in  amperes.  An  in- 
spection of  the  figure  will  show  that  the 
peak  of  the  load,  that  is,  the  maximum  load 
of  the  curve,  occurred  at  5.30  p.  M.  when  it 
exceeds  1,700  amperes,  while  an  hour  and 
a  half  earlier,  or  at  4  p.  M.,  it  was  800 
amperes,  and  an  hour  and  a  half  later,  or  at 
7  P.  M.,  it  was  930  amperes.  At  8.30  p.  M. 
the  load  has  increased,  perhaps,  owing  to 
the  lighting  of  some  theatre,  after  which 
the  load  steadily  falls  until  2.30  A.  M.  The 
average  load  during  the  twenty -four  hours 
from  this  diagram  is  620  amperes,  and  since 
the  maximum  load  is  1,710,  the  ratio  of  the 
average  to  the  maximum  is  0.363  or  36.3 
per  cent.  This  is  called  the  load  factor. 

If  the  load  represented  in  Fig.  118,  were 
supplied  without  the  aid  of  a  storage  bat- 
tery, it  would  be  necessary  to  install  boil- 


STORAGE   BATTERIES.  349 

ers,  dynamos  and  engines  to  the  extent 
necessary  to  supply  a  current  of  1,700 
amperes,  although  the  average  load  is  only 
620.  By  the  use  of  a  storage  battery, 
capable  of  supplying  800  amperes  for, 
say  four  hours ;  or,  a  battery  having 
a  storage  capacity  of  4  x  800  =  3,200 
ampere-hours,  then  the  maximum  load 
which  the  boilers,  engines  and  dynamos 
would  have  to  supply  would  be  900 
amperes  \  or,  only  about  half  as  much 
as  in  the  preceding  case,  while  the  load 
during  the  daytime  would  be  increased 
by  the  amount  necessary  to  charge 
the  storage  batteries.  Good  practice  re- 
quires that  the  charging  be  done  during  the 
time  of  the  day  when  the  load  is  the  least ; 
or,  in  this  case,  between  the  hours  of  1  and  7 
A.  M.  The  smaller  the  load  factor  the  greater 
the  probability  of  obtaining  economy  in 
the  installation  of  a  storage  battery. 


350      ELECTRIC   INCANDESCENT  LIGHTING. 

Another  case  arises  in  which  an  advan- 
tage is  derived  from  the  use  of  a  storage 
battery ;  namely,  where  the  engines  and 
boilers  employed  to  drive  the  dynamo  are 
used  during  the  hours  of  darkness  only, 
and  are  stopped  during  the  day,  while  it  is 
desired  to  maintain  a  few  lamps  during 
the  daytime.  Under  these  circumstances 
it  is  often  more  economical  to  establish  a 
storage  battery  plant,  which  can  be  charged 
during  the  time  of  running  at  night,  thus 
permitting  the  engine  and  dynamo  to  be 
stopped  during  the  daytime  and  the  stor- 
age battery  to  supply  the  few  lights 
required. 

Before  proceeding  to  the  general  descrip- 
tion of  a  storage  battery  installation,  it 
may  be  well  to  describe  briefly  the  princi- 
ples of  its  operation.  A  storage  cell  differs 
in  no  respect  from  an  ordinary  voltaic  cell ; 


»T  *$ 

PHCFLRTY  CF 


351 


for,  like  a^iftaieHgytj^fiafi^^  essentially 
of  two  plates  or  elements,  called  respectively 
the  positive  and  the  negative  plate,  plunged 
in  an  acid  liquid  or  electrolyte  capable  of 
acting  on  one  of  the  plates.  As  the  result 
of  the  chemical  action  that  occurs  under 
these  circumstances,  an  electric  current  is 
produced  which  passes  in  a  definite  direc- 
tion through  the  electrolyte  and  issues  from 
the  cell  at  one  of  its  terminals  or  poles 
and  returns  to  it,  after  having  passed 
through  the  circuit  in  which  the  cell  is  con- 
nected, by  the  other  terminal  or  pole.  In 
both  the  ordinary  voltaic  and  the  storage 
cell,  exhaustion  takes  place  when  a  certain 
output  of  electricity  is  yielded.  In  the 
case  of  the  voltaic  cell  both  the  liquid,  and 
at  least  one  of  the  plates,  must  be  renewed, 
while  in  the  case  of  the  storage  cell,  all 
that  is  necessary  for  renewal  is  to  connect 
the  terminals  of  the  cell  with  an  independ- 


352      ELECTRIC   INCANDESCENT   LIGHTING. 

ent  electric  source,  and  send  a  current 
through  it  in  the  opposite  direction  to  that 
of  the  current  it  yields.  This  current  is 
called  the  charging  current,  and  the  cell  re- 
ceiving it  is  said  to  be  charged.  Since  a 
storage  cell  thus  derives  its  energy  second- 
arily from  some  other  electric  source,  it  is 
sometimes  called  a  secondary  cell,  in  contra- 
distinction to  a  primary  or  voltaic  cell. 

A  great  number  of  storage  cells  have 
been  devised.  Practically  all  that  have 
been  placed  in  commercial  use,  consist  of 
perforated  lead  plates  or  grids,  correspond- 
ing to  the  positive  and  negative  plates  of 
the  voltaic  cell,  with  the  perforations  filled, 
respectively,  with  peroxide  of  lead  and 
finely  divided  metallic  lead.  These  plates 
are  associated,  or  placed  side  by  side,  in  a 
solution  of  sulphuric  acid  and  water.  In 
the  original  form  given  to  these  cells,  they 


STORAGE  BATTERIES.  353 

consisted  of  a  very  large  positive  and  nega- 
tive plate,  suitably  supported  at  a  short 
distance  from  each  other,  and  then  rolled 
up  together  in  a  close  spiral.  It  was 
found,  however,  in  practice,  that  when 
such  a  plate  became  damaged  in  one  part, 
the  entire  cell  had  to  be  rejected,  so  that 
for  the  purpose  of  convenience,  as  well  as 
for  the  ready  inspection  of  the  different 
parts  of  the  plate,  they  are  now  generally 
made  in  a  number  of  smaller  plane  plates, 
placed  parallel  to  one  another,  which, 
when  connected  in  parallel,  are  equivalent 
to  two  large  plates  of  the  same  total  sur- 
face. 

The  simplest  form  of  such  a  cell  would 
consist  of  a  single  positive  and  a  single 
negative  plate,  placed  side  by  side ;  but 
since  the  positive  plate  would  only  have  a 
negative  plate  on  one  side  of  it,  the  other 


354      ELECTRIC   INCANDESCENT  LIGHTING. 

side  being  uncovered,  it  is  preferable  to 
associate  two  negative  plates  with  one  posi- 
tive plate,  so  as  to  utilize  the  entire  surface 
of  the  positive  plate.  Such  a  cell  is  shown 
in  Fig.  119,  where  two  negative  plates,  JV", 
are  placed  one  on  each  side  of  a  single  posi- 
tive plate  P,  inside  a  jar  e7W,  filled  to 
a  convenient  height  with  sulphuric  acid 
and  water.  The  positive  plate  is  shown 
separately  at  A.  It  consists  of  a  grid  or 
frame  of  antimonious  lead ;  i.  e.,  lead 
alloyed  with  a  small  amount  of  antimony, 
so  as  to  keep  it  from  being  acted  upon  by 
the  acid  liquid.  In  this  frame  are  shown 
eight  small  circular  buttons  a,  filling  circu- 
lar holes  in  the  grid.  These,  when  the  cell 
is  charged,  consist  of  peroxide  of  lead,  and 
constitute  the  active  material  of  the  cell. 
The  negative  grids  have  apertures  filled 
with  square  buttons,  which  when  in  the 
charged  condition  are  filled  with  porous 


STORAGE  BATTERIES. 


355 


FIG.  119. — SMALL  STORAGE  CELL. 


356      ELECTRIC    INCANDESCENT   LIGHTING. 

lead.  In  the  cell  shown,  the  plates  are 
three  inches  square,  and  the  weight  of  the 
entire  cell,  filled  with  solution,  is  four 
pounds.  The  capacity  of  this  cell  is  about 
6  ampere-hours  when  discharged  at  normal 
rates. 

In  a  fully  charged  storage  cell,  the  ma- 
terials filling  the  apertures  in  the  grids  are 
dissimilar ;  namely,  peroxide  of  lead  and 
metallic  lead.  During  discharge  chemical 
actions  occur,  which  result  in  reducing 
these  substances  to  the  same  substance  ; 
namely,  monoxide  of  lead.  When  now 
the  charging  current  is  sent  through  the 
exhausted  cell,  a  dissimilarity  is  again 
produced,  the  monoxide  being  converted  to 
peroxide  of  lead  on  the  positive  plate,  and 
into  porous  lead  on  the  negative  plate.  It 
is  evident,  therefore,  that  it  is  not  electric- 
ity which  is  stored,  but  energy  in  the  form 


STORAGE   BATTERIES.  357 

of  chemical  energy,  and  in  a  form  capable, 
on  discharge,  of  being  released  under  suit- 
able conditions  as  electric  energy. 

Fig.  120,  shows  a  larger  size  of  the  same 
type  of  storage  cell.  Here  five  positive 
plates  are  associated  alternately  with  six 
negative  plates,  so  that  both  external  plates 
are  negative ;  these  plates  are  provided 
with  rectangular  apertures.  The  plates 
are  bound  together  by  an  insulating  frame 
F,  F,  F,  and  are  individually  separated  or 
maintained  at  the  proper  distance  apart- by 
sheets  of  asbestos.  In  the  cell  shown,  the 
plates  are  10.5"  square,  and  the  entire  cell, 
with  solution,  weighs  170  pounds.  Its 
normal  capacity  is  500  ampere-hours,  or, 
approximately,  3  ampere-hours  per  pound 
of  total  weight.  All  the  positive  plates 
are  connected  together  to  form  a  single 
positive  plate  with  terminal  P,  and  all  the 


358      ELECTKIC   INCANDESCENT  LIGHTING. 


FIG.  120. — STORAGE  CELL. 


STORAGE   BATTERIES. 


359 


negatives  are  similarly  connected  to  form 
a  single  negative  terminal  N. 

When  storage  cells  are  employed  in  large 
central  stations  for  the  supply  of  powerful 


FIG.  121. — LARGE  STORAGE  CELL. 

currents,  it  is  customary  to  associate  large 
plates  in  single  cells,  rather  than  to  employ 
a  number  of  smaller  cells  in  parallel.  Fig. 


360      ELECTRIC    INCANDESCENT    LIGHTING. 

121,  represents  a  form  of  large  cell  for  such 
an  apparatus.  Instead  of  employ  ing  a  glass 
jar,  the  containing  vessel  is  of  wood,  with 
an  interior  leaden  lining.  Here  21  nega- 
tive plates  are  associated  with  20  positive 
plates,  each  plate  is  15.5"  square,  and  the 
total  weight  of  the  cell,  when  filled  with 
solution,  is  800  pounds.  The  normal 
capacity  of  this  cell  is  5,000  ampere-hours, 
or  about  6.4  ampere-hours  per  pound  of 
total  weight. 

It  is  evident  that  the  storage  capacity 
increases  with  the  weight  of  the  cells ; 
being  over  6  ampere-hours  per  pound, 
with  larsre  cells,  and  with  the  smallest  cells 

O  7 

about  1  1/2  ampere-hours  per  pound  of 
total  weight.  The  E.  M.  F.  produced  by 
the  average  storage  cell  is  about  2  volts. 
When  fully  charged,  while  discharging,  it 
is  about  2.2  volts,  and  falls  during  dis- 


charge 

energy  wcia^  ex- 

pressed in  watt-hours  is,  therefore,  approx- 
imately, 2  multiplied  by  the  capacity  of 
the  cell  in  ampere-hours.  Thus  the  cell 
last  mentioned  has  an  energy  storage 
capacity  of  2  X  5,000  =  10,000  watt- 
hours,  or  10  KW-hours,  under  normal 
circumstances. 

Since  incandescent  electric  lamps  gener- 
ally require  a  pressure  of  about  115  volts, 
and  since  a  single  storage  cell  has  only  2 
volts  E.  M.  R,  it  is  necessary  to  couple  at 
least  57  cells  in  series,  and,  in  order  to  al- 
low for  drop  of  pressure  in  the  feeders, 
mains  and  house  wires,  the  usual  number 
required  for  this  purpose  is  from  60  to  65 
cells.  For  three-wire  installations,  twice 
this  number  is  necessary,  or  about  120 
cells.  Such  a  three-wire  storage  battery 


STORAGE   BATTERIES.  363 

installation  is  represented  in  Fig.  122. 
The  cells  are  arranged  in  series,  the  posi- 
tive terminal  of  one  cell  being  connected  to 
the  negative  terminal  of  the  next.  Each 
cell  has  11  plates,  5  positive  and  6  nega- 
tive, and  the  normal  capacity  of  the  cell  is 
1,000  ampere-hours,  giving  a  10-hour  dis- 
charge at  the  rate  of  100  amperes. 

A  storage  battery  plant  requires  for  its 
convenient  operation  a  switchboard  with  its 
accessories,  such,  for  example,  as  is  shown 
in  Fig.  123.  S,  &,  are  two  double-pole 
switches,  one  for  controlling  the  charging, 
and  the  other  the  discharging  circuit.  The 
charging  here  being  performed,  as  is  usual 
in  such  cases,  by  a  dynamo  whose  pressure 
is  controlled  by  the  field  rheostat  operated 
by  a  handle  at  F.  A,  A,  are  ammeters  in 
the  charging  and  discharging  circuits ;  V,  is 
a  voltmeter  which  by  means  of  ihepressure 


364      ELECTRIC   INCANDESCENT   LIGHTING. 


B 


e> 


# 

FIG.  123. — STORAGE  BATTERY  SWITCHBOARD. 

gwitch  P,  can  be  connected  either  to  the 
dynamo  terminals,  or  to  the  battery  termi- 
nals, to  show  the  pressure  before  the  switch 
•is  thrown.  T,  is  an  automatic  cut-out  which 


STORAGE   BATTERIES.  365 

disconnects  the  charging  circuit  of  the 
dynamo,  as  soon  as  the  C.  E.  M.  F.  of 
the  cells  exceeds  the  E.  M.  F.  of  the  dynamo, 
and  0,  is  an  overload  switch  in  the  dis- 
charging circuit,  arranged  automatically  to 
break  the  circuit  of  the  battery  should  the 
discharge  become  excessive.  It,  is  a  switch 
which  may  either  be  used  to  throw  in  and 
out  reserve  cells,  in  order  to  maintain  the 
discharging  pressure  constant,  or  to  throw 
in  and  oqt  C.  E.  M.  F.  cells,  that  are 
employed  in  place  of  the  rheostat  in  the 
lamp  circuit  during  charge. 

The  overload  switch  is  shown  in  greater 
detail  in  Fig.  124.  Here  a  coil  of  heavy 
wire  (7, — pivoted  upon  its  axis,  has  its 
ends  dipping  in  mercury  cups.  The  coil 
is  placed  in  the  main  circuit  of  discharge 
in  such  a  manner  that  when  the  discharg- 
ing current  becomes  excessive,  the  electro- 


366      ELECTRIC   INCANDESCENT   LIGHTING. 

magnetic  force  developed  by  the  coil  rotates 
tlie  helix  and  lifts  the  contact  points  P,  P, 


FIG.  124.— OVERLOAD  SWITCH. 

out  of  the  mercury  cups.     H,  is  the  handle 
for  restoring  the  circuit  when  desired. 

Fig.  125,  shows  &  form  of  overload  switch 
suited  for  heavier  currents.  The  spring 
jaws,  J,  J,  are  in  contact  with  the  plates 
7J  T,  when  the  switch  is  closed,  and  the 
discharging  circuit  established.  S,  S9  are 


STORAGE  BATTERIES. 


FIG.  125.— OVERLOAD  SWITCH,  CLOSED. 

spiral  springs  which  tend  to  disengage  the 
plates  and  open  the  switch,  but  whose  ac- 
tion is  prevented  by  the  armature  J.,  which 


368      ELECTRIC   INCANDESCENT   LIGHTING. 

normally  holds  the  switch  plates  in  posi- 
tion. The  coil  C,  of  heavy  conductor,  is 
placed  in  the  discharging  circuit,  and,  as 
soon  as  the  current  strength  exceeds  a  cer- 
tain safe  limit,  it  attracts  the  armature  A, 
to  the  iron  pofe  piece  P,  thus  allowing  the 
springs  &,  S  to  act,  and  the  plates  T,  T,  to 
be  thrown  out  of  the  jaws  J,  J,  as  shown 
in  Fig.  126. 

In  order  to  maintain  a  storage  battery 
in  proper  working  order,  it  is  necessary  to 
test  the  individual  cells  from  time  to  time, 
for  E.  M.  F.  This  is  readily  effected  in 
practice,  by  means  of  any  suitable  voltmeter 
connected  with  electrodes  for  application 
to  each  separate  cell.  A  convenient  form 
of  apparatus  for  this  purpose  is  shown  in 
Fig.  127.  A  simpler  form  of  testing  ap- 
paratus, not  so  accurate  as  the  preceding, 
is  shown  in  Fig.  128.  It  consists  of  a  pair 


STORAGE   BATTERIES. 


FIG.  126.— OVERLOAD  SWITCH, 
RELEASED. 


370    ELECTRIC  INCANDESCENT  LIGHTING. 

of  handles  with  sharp  metallic  points,  to 
make  connection  with  the  leaden  electrodes 
of  the  cells,  and  connected  by  a  loop  of 


FIG.  127. — STORAGE  CELL  VOLTMETER  AND  ELECTRODES. 

wire.  In  the  end  of  one  of  the  handles  is 
a  lamp  socket  in  which  a  low  volt  lamp 
is  inserted.  If  the  cell  tested  is  in  good 


STORAGE  BATTERIES.  371 


FIG.  128.— SIMPLE  FORM  OF  STORAGE  CELL  TESTER. 


372      ELECTRIC   INCANDESCENT   LIGHTING. 

order  its  E.  M.  F.  will  be  sufficient  to  bring 
the  lamp  up  to  candle-power. 

The  efficiency  of  a  storage  cell  or  battery 
is  the  ratio  of  the  output  to  the  intake. 
An  ideally  perfect  battery  would  lose  no 
energy,  and  would,  therefore,  have  the 
same  intake  and  output,  representing  an 
efficiency  of  unity,  or  one  hundred  per  cent. 
In  practice,  the  ampere-hour  efficiency  of  a 
storage  cell  may  be  over  ninety-five  per 
cent,  so  far  as  regards  electric  quantity 
or  ampere-hours,  that  is  to  say,  if  100 
ampere-hours  be  supplied  to  a  storage 
battery  during  charge,  it  may  yield  more 
than  95  ampere-hours  during  discharge. 
On  the  other  hand,  since  the  pressure  at 
the  terminals  of  a  cell  during  charge  is 
over  2  volts,  rising  toward  full  charge  to 
2  1/2  volts,  while  the  pressure  during  dis- 
charge is  from  2.2  to  1.8  volts,  the  energy 


STORAGE   BATTERIES.  373 

efficiency,  as  reckoned  from  the  watt-hour 
output,  is  considerably  less,  and  usually 
varies  from  seventy-five  to  eighty -five  per 
cent,  according  to  the  conditions  of  the 
charge  and  discharge.  A  battery  dis- 
charged at  a  rapid  rate  will  not  have  so 
high  an  efficiency,  either  in  quantity  or  in 
energy,  as  if  slowly  discharged.  In  relation, 
therefore,  to  coal  consumed,  the  efficiency  of 
a  storage  battery  is  about  eighty  per  cent., 
but  in  relation  to  ampere-hours  the  effi- 
ciency may  be  over  ninety-five  per  cent. 


CHAPTER  XVIII. 

SERIES    INCANDESCENT    LIGHTING. 

WE  have  have  hitherto  described  mul- 
tiple-connected lamps  ;  or,  in  the  case  of 
the  three- wire  system,  lamps  in  series-mul- 
tiple. It  sometimes  happens,  that  a  dis- 
trict to  be  lighted  is  scattered  and  wide 
spread,  so  that  scattered  lamps  have  to 
be  supplied  at  considerable  distances  from 
the  central  station.  As  we  have  already 
shown,  under  these  circumstances  a  very 
great  amount  of  copper  would  require  to 
be  employed  in  their  multiple-distribution. 
In  order  to  avoid  this,  a  series  distribu- 
tion is  sometimes  adopted.  Here,  as  we 
have  already  described,  a  number  of  sep- 
arate lamps  are  connected  in  series  in  one 


374 


SEKIES   INCANDESCENT   LIGHTING.       375 

circuit.  Since  in  such  a  system  of  distri- 
bution the  extinguishment  of  a  single  lamp 
would  open  the  entire  circuit,  a  simple  au- 
tomatic safety  device  is  required,  which 
will  establish  a  short  circuit  about  the 
faulty  lamp,  in  case  it  breaks,  thus  pre- 
serving the  continuity  of  the  circuit. 

A  system  of  series-distributed  incan- 
descent lamps  may  be  operated  from  a 
constant  high-potential  dynamo.  Thus,  a 
dynamo  of  1,000  volts  E.  M.  F.  may  operate 
a  circuit  of  30  incandescent  lamps,  each 
having  a  pressure  of  33  1/3  volts,  includ- 
ing drop  in  connecting  wires.  Several 
such  1,000- volt  circuits  may  be  arranged  in 
parallel,  thus  producing  a  multiple-series 
system  of  distribution,  as  shown  in  Fig. 
129. 

Such  a  series-connected  system  is  some- 


376      ELECTKIC   INCANDESCENT   LIGHTING. 

times  used  for  incandescent  lamps  in  street 
lighting.  It  is  not  suitable  for  house 
lighting,  since  it  is  essential  that  the  num- 
ber of  lamps  in  each  series  circuit  should 


a         b         c         d 
129. — MULTIPLE-SERIES  SYSTEM. 

be  as  nearly  constant  as  possible,  and  this 
precludes  the  possibility  of  cutting  lamps 
out  of  a  circuit  when  no  longer  required. 

Various  forms  of  automatic  circuit-pro- 
tecting devices  have  been  produced.  One 
of  the  simplest  of  these,  called  the  film 
cut-out,  consists  of  a  thin  strip  of  paper 
placed  between  two  spring  contacts  con- 


SERIES   INCANDESCENT   LIGHTING.      377 

nected  with  two  terminals  of  each  lamp. 
While  the  lamp  remains  lighted,  the  elec- 
tric pressure  across  the  thickness  of  the 
strip  of  paper  is  only  a  few  volts ;  i.  e.,  the 
pressure  at  the  lamp  terminals,  but  if  the 
filament  should  break,  the  pressure  at  the 
terminals  is  the  full  pressure  of  the  circuit 
which  may  be  1,000  volts.  This  pressure 
is  capable  of  piercing  the  thin  paper  sheet, 
thus  establishing  an  arc,  which  instantly 
welds  the  two  metal  strips  together,  thus 
short-circuiting  the  lamp  and  re-establish- 
ing the  circuit. 

As  already  stated,  series  incandescent 
lamps  are  generally  employed  for  out-door 
lighting  and,  therefore,  have  to  be  pro- 
tected from  the  weather.  The  compara- 
tively high  electric  pressure  employed  on 
these  circuits,  not  being  safe  to  handle 
under  all  conditions,  requires  certain  pre- 


378      ELECTRIC   INCANDESCENT  LIGHTING. 

cautions  in  insulation  when  introduced 
into  buildings.  Fig.  130,  shows  a  form  of 
lamp  and  fixtures  suitable  for  out-door 
series-incandescent  lighting.  The  lamp  Z, 


FIG.  130. — STREET  FIXTURE,  WITH  SERIES  INCANDESCENT 
LAMP. 

is  placed  in  its  socket  beneath  tne  porce- 
lain deflector  D,  which  not  only  serves  to 
scatter  and  reflect  the  light,  but  also,  in 
conjunction  with  the  cover  (7,  to  protect  the 


SERIES   INCANDESCENT   LIGHTING.       379 

lamp  socket  from  rain.  The  circuit  wires 
Cj  c,  are  brought  to  the  socket  of  the  lamp 
after  being  secured  to  the  insulators  I,  I. 
Fig.  131,  shows  the  same  fixture  with  the 


FIG.  131. — STREET  FIXTURE,  WITH  LAMP  REMOVED  AND 
SOCKET  EXPOSED. 

deflector  D,  removed,  showing  the  socket 
>9,  placed  in  the  interior.  Fig.  132  shows 
a  form  of  lamp  post  suitable  for  street 
lighting  with  such  lamps.  Another  form 


380      ELECTKIC   INCANDESCENT   LIGHTING. 


FIG.  132.— LAMP  POST. 


SERIES   INCANDESCENT   LIGHTING.      381 

of  fixtures  is  shown  in  Fig.  133;  here  the 
incandescent  lamp  is  provided  with  an 
external  globe. 

Where  a  series  circuit  has  already  been 
installed    for   operating    arc    lamps,  it  is 


FIG.  133. — STREET  LAMP  FIXTURE. 

sometimes  desirable  to  insert  incandescent 
lamps  in  the  same  circuit.  This  is  done 
by  employing  series  incandescent  lamps  of 
special  manufacture.  Since  the  current 
strength,  in  a  series-arc  circuit,  is  usually 


382      ELECTRIC   INCANDESCENT  LIGHTING. 

about  10  amperes,  and  is  the  same  in  all 
parts  of  the  circuit,  it  is  necessary  that  the 
incandescent  lamps  be  made  for  this  cur- 
rent strength.  A  fifty-watt  16-candle 
power  lamp,  taking  10  amperes,  must  be  a 
5-volt  lamp,  since  5  volts  X  10  amperes  = 
50  watts.  Consequently,  the  resistance 
of  the  lamp  must  be  only  1/2  ohm,  since  10 
amperes  X  1  /2  ohm  =  5  volts,  and  the 
filament  must  be  comparatively  short  and 
thick  in  order  to  possess  this  relatively 
low  resistance.  It  is  evident  that  lamps 
of  different  candle  power  can  be  obtained 
from  the  use  of  such  series  circuits,  by 
suitably  adjusting  the  resistance  of  their 
filaments.  The  connections  for  such  a 
series  arc  and  incandescent  circuit  are 
shown  in  Fig.  134. 

Since   series-arc  circuits  frequently  em- 
ploy   dangerously    high  pressures,   it   be- 


SERIES   INCANDESCENT   LIGHTING.      383 

comes  unsafe  to  come  in  contact  with  the 
conductors  of  such  circuits  when  standing 
on  wet  ground ;  for,  such  circuits  com- 


FIG.  134. — SERIES  ARC  AND  INCANDESCENT  CIRCUIT. 

moiily  have  marked  leakage  and  thus  a 
dangerously  high  current  might  be  sent 
through  the  body.  Consequently,  it  is 


384      ELECTRIC   INCANDESCENT   LIGHTING. 

necessary  carefully  to  insulate  the  keys 
and  connections  of  incandescent  lamps 
operated  on  arc  circuits. 


FIG.  135. — LAMP  FOR  SERIES-ARC  CIRCUIT,  WITH 
CUT-OUT  SWITCH. 


SERIES    INCANDESCENT   LIGHTING.       885 

Fig.  135,  shows  a  form  of  lamp  suit- 
able for  series-arc  circuits.  Like  all 
series-connected  lamps,  it  contains  an  au- 
tomatic cut-out,  and  of  the  film  type  al- 
ready described.  It  has  no  key,  but  is 
provided  with  a  ceiling  switch  whereby 
it  may  be  short-circuited  and  thus  extin- 
guished. 


CHAPTER  XIX. 

ALTERNATING-CURRENT    CIRCUIT    INCAN- 
DESCENT  LIGHTING. 

SINCE  incandescent  lamps  are  frequently 
operated  on  alternating-current  circuits,  it 
may  be  well  briefly  to  discuss  some  of  tlie 
characteristics  of  these  currents  and  in- 
stances of  their  commercial  application. 

In  a  continuous  current  the  direction  of 
electric  flow  does  not  change.  Its  strength 
may  vary  periodically,  in  which  case  the 
current  is  said  to  pulsate;  or,  it  may  be 
unvarying,  in  which  case  the  current  is 
said  to  be  steady.  An  alternating  current, 
on  the  contrary,  changes  direction  many 


NATING-CUKKENT   OIROU 


times  in  a^s^jtrftfJ,  f%ep$  being  first' a  wave 
or  flow  of  curreStHlrro^^r'tEe  circuit  in 
one  direction,  and  then  a  wave  or  flow 
of  current  in  the  opposite  direction,  and 
so  on.  Each  of  these  waves  or  flows  is 
called  an  alternation,  and  a  complete  to- 
and-fro  motion,  or  double  wave,  is  called 
a  cycle.  The  frequency  of  alternation  is 
the  number  of  alternations  or  of  cycles 
executed  in  a  second ;  thus  ordinary  com- 
mercial alternating  circuits  have  a  fre- 
quency of  from  25  cycles,  or  50  alternations 
per  second,  to  140  cycles,  or  280  alterna- 
tions per  second.  The  number  of  cycles, 
or  complete  periods,  is  sometimes  symbol- 
ized by  the  sign  ~,  so  that  a  frequency  of 
140  complete  periods,  or  cycles,  per  second 
would  be  written  140  ~. 

Between  each  pair  of  successive  waves, 
at   the   time   when   the  current  is  chang- 


388      ELECTKIC   INCANDESCENT  LIGHTING. 

ing  direction,  there  is  no  current  flowing 
in  the  circuit.  Consequently,  it  might  be 
supposed,  when  an  alternating  current, 
of  say  120  ~,  is  sent  through  a  lamp,  since 
there  would  be  240  moments  in  each 
second  when  no  current  is  flowing,  that 
the  light  furnished  by  the  lamp  would 
pulsate,  being  extinguished  and  relighted 
240  times  in  a  second.  In  point  of  fact, 
this  tendency  to  pulsate  does  exist;  but 
when  the  frequency  is  sufficiently  high, 
before  the  filament  loses  enough  of  its  heat 
to  cease  glowing,  it  receives  a  fresh  acces- 
sion of  heat  from  the  succeeding  wave 
of  current.  Moreover,  the  retina  of  the 
eye  tends  to  retain  its  luminous  impres- 
sions for  a  sufficiently  great  fraction  of  a 
second  to  aid  in  the  apparent  uniformity 
of  the  light.  The  result  is,  when  the  fre- 
quency is  above  say  30  ~,  or  60  alterna- 
tions per  second,  i.  e.,  3,600  alternations 


ALTERNATING-CURRENT   CIRCUIT.        389 

per  minute,  that  the  light  of  an  incandes- 
cent lamp  is  practically  steady.  As  the 
frequency  is  reduced,  the  higher  economy 
lamps  ;  i.  e.,  those  which  have  a  greater 
efficiency,  or  a  greater  number  of  candles- 
per-watt,  are  the  first  to  suffer  in  apparent 
steadiness.  First,  because  they  are  more 
brilliant  for  the  same  candle-power,  or  are 
operated  at  a  high  temperature,  and  the 
eye  is  much  more  sensitive  to  changes 
of  brilliancy  than  to  changes  of  candle- 
power,  or,  in  other  words,  to  changes  in 
candle-power  per  square  inch  of  bright 
surface,  than  to  total  candle-power;  and 
second,  because  such  lamps  have  usually 
thinner  filaments,  and  hence  chill  more 
rapidly. 

The  frequency  employed  in  alternating- 
current  circuits  varies  between  25  ~  and 
140  ~  per  second. 


390      ELECTRIC    INCANDESCENT   LIGHTING. 

If  an  incandescent  lamp  be  supplied  by 
a  continuous  pressure,  of  say  110  volts, 
and  gives  a  candle-power  of  16  candles  at 
this  pressure,  then  if  it  be  removed  and 
connected  with  an  alternating-current  pres- 
sure of  110  volts,  it  will  shine  with  equal 
brightness  and  give  16  candles  as  before, 
no  matter  what  the  frequency,  provided 
only  that  the  frequency  be  sufficiently 
great  to  keep  the  lamp  from  flickering. 
Similarly,  the  current  strength,  which  the 
lamp  will  take,  on  an  alternating  current 
circuit,  is  the  same  as  that  which  it  takes 
on  a  continuous-current  circuit.  This  is 
for  the  reason  that  although  the  strength 
of  an  alternating  current  is  constantly 
fluctuating,  between  the  apex  of  the  suc- 
cessive waves  and  zero  at  the  moments  of 
reversal,  yet  the  current  is  defined  or 
measured  by  its  heating  effect,  so  that  if 
half  an  ampere  of  continuous  current 


ALTERNATING-CURRENT   CIRCUIT.       391 

brings  a  given  lamp  to  candle-power,  then 
the  alternating-current  strength  which  also 
brings  the  lamp  to  candle-power,  will  be 
half  an  ampere,  no  matter  what  the  outline 
of  the  current  wave  may  be.  Thus,  it 
would  be  possible  for  each  wave  to  have  a 
current  strength  of  2  amperes  at  the  apex, 
and  yet  to  produce  only  the  average  heat 
effect  of  a  half  an  ampere.  Such  a  current 
would  have  an  effective  current  strength 
of  1/2  ampere.  In  general,  the  maximum 
current  strength  is  about  forty  per  cent,  in 
excess  of  the  effective  current  strength,  so 
that  when  an  alternating-current  ammeter 
shows  that  a  current  of  one  effective 
ampere  is  passing  in  a  circuit,  the  apex  of 
the  successive  current  waves  will,  probably, 

attain    a  strength    of  1 —    amperes.      In 

the  same  way,  if  the  pressure  in  an  alter- 
nating-current circuit,  as  shown  by  lamps 


392      ELECTRIC    INCANDESCENT   LIGHTING. 

or  by  instruments,  be  100  volts,  the  instan- 
taneous maximum  value  in  the  successive 
cycles  will,  probably,  be  about  140  volts. 

It  is  evident,  therefore,  that  it  would 
be  possible  to  employ  alternating-current 
generators  instead  of  continuous-current 
generators,  in  a  central  station,  for  the  dis- 
tribution of  electric  light.  The  drop  of 
pressure,  however,  in  the  supply  feeders 
and  mains,  would,  in  such  a  case,  for  reasons 
that  it  is  not  necessary  here  to  consider,  be 
greater  than  with  the  same  strength  of 
continuous  current,  and  it  is  generally  con- 
sidered, that  it  is  disad  vantageous  to  supply 
low-tension  systems  of  incandescent  light- 
ing from  alternating-current  generators. 
When,  however,  the  lighting  has  to  be  dis- 
tributed at  great  distances,  and,  therefore, 
at  a  high  electric  pressure,  in  order  to  avoid 
expense  in  conductors,  the  alternating-cur- 


ALTERNATING-CURRENT   CIRCUIT.       393 

rent  system  possesses  decided  advantages, 
since  it  readily  lends  itself  to  transforma- 
tion of  pressure;  that  is  to  say,  it  is  easy 
to  take  an  alternating-current  generator  of 
say  2,000  volts  E.  M.  F.,  and  to  transmit 
this  pressure  to  considerable  distances  over 
comparatively  small  conductors,  and  then 
to  reduce  the  pressure  locally,  within  the 
precincts  of  buildings,  to  say  100  volts,  by 
means  of  an  apparatus,  called  an  alternat- 
ing-current transformer. 

A  form  of  alternating-current  trans- 
former is  shown  in  Fig.  136.  Such  an 
apparatus  consists  essentially  of  two  coils 
of  insulated  wire,  wound  around  a  common 
laminated  iron  core.  These  coils  are  con- 
nected respectively  with  a  high-pressure 
and  a  low-pressure  circuit.  In  this  case, 
the  high-pressure  circuit  is  the  source  of 
energy,  or  i\\z  primary  circuit,  and  the  low- 


394      ELECTRIC   INCANDESCENT   LIGHTING. 

pressure  circuit  is  the  circuit  of  delivery,  or 
the  secondary  circuit.  The  effect  of  send- 
ing an  alternating  current  through  the 
primary  coil  is  to  induce  alternations  of 


L,.  .  ^_ 


FIG.  136.— ALTERNATING-CURRENT  TRANSFORMER. 
CAPACITY  1  KW,  OR  20  50- WATT  LAMPS. 

the  same  frequency,  but  different  E.  M.  R, 
in  the  secondary  coil.  If  the  secondary 
coil  contains  more  turns  than  the  primary, 
then  the  secondary  E.  M.  F.  is  the  greater. 
If,  on  the  contrary,  as  in  this  case,  the 


ALTERNATING-CURRENT   CIRCUIT.       395 

secondary  turns  are  fewer,  then  the  second- 
ary E.  M.  F.  will  be  lower.  Transformers 
are,  therefore,  of  two  kinds ;  namely,  step-up 
transformers,  or  those  which  raise  the  pres- 
sure, and  step-down  transformers,  or  those 
which  lower  it. 

Like  all  machines  for  effecting  the  trans- 
formation of  energy,  alternating-current 
transformers  waste  some  portion  of  what 
they  receive.  In  large  transformers  this 
loss  at  full  load  is  relatively  very  small,  only 
about  two  per  cent.,  so  that  the  efficiency 
of  a  large  transformer,  at  full  load,  is 
approximately  ninety-eight  per  cent.  On 
the  other  hand,  the  relative  loss  at  very  light 
load  is  necessarily  much  greater.  During 
the  day  time,  when  comparatively  few 
lamps  are  lighted  over  the  distribution 
system,  the  power  supplied  to  magnetize 
the  transformers  may  be  considerably 


396      ELECTRIC    INCANDESCENT    LIGHTING. 

greater  than  the  power  usefully  expended. 
This  is  the  only  objection  to  the  action 
of  alternating-current  transformers,  and  is 
outweighed  when  the  distance  to  which 
the  current  has  to  be  carried  is  sufficiently 
great,  since,  otherwise,  a  large  amount  of 
copper  would  have  to  be  employed  to 
transmit  the  necessary  energy  in  any  other 
way.  A  continuous  current  cannot  be 
transformed  without  the  aid  of  rotating 
mechanism. 

In  Fig.  136,  P,  P,  are  the  primary  wires 
leading  to  the  high-pressure  mains,  which 
are  usually  supported  on  poles  overhead. 
S,  8,  are  the  secondary  wires  leading  to  the 
interior  of  the  building  and  acting  as  ser- 
vice wires.  The  apparatus  represented  in 
the  figure  has  a  capacity  of  1  KW,  and, 
therefore,  is  capable  of  supplying  about 
20  fifty-watt  incandescent  lamps.  If  the 


ALTERNATING-CURRENT    CIRCUIT.       397 

secondary  pressure  be  100  volts,  the  cur- 
rent strength  at  full  load  would  be  10  am- 
peres approximately,  since  100  volts  X  10 
amperes  =  1,000  watts.  In  the  primary 
circuit  the  current  strength  will  be  about 
1  ampere  at  full  load,  if  the  primary 
pressure  be  1,000  volts,  since  1,000  volts 
X  1  ampere  =  1,000  watts.  In  reality, 
owing  to  some  loss  of  power  in  the  trans- 
former, say  50  watts,  the  current  strength 
would  be  somewhat  in  excess  of  1  ampere. 
Moreover,  in  alternating-current  circuits, 
the  current  strength  is  in  excess  of  the 
number  of  amperes  which,  multiplied  by 
the  pressure  in  volts,  gives  the  actual 
activity  in  watts. 

Transformers  of  small  size,  weight  and 
capacity,  are  more  expensive  per  KW,  or 
per  lamp,  both  to  purchase  and  to  operate 
than  large  transformers,  since  they  require 


398      ELECTRIC   INCANDESCENT   LIGHTING. 

relatively  more  labor  and  material  and  have 
a  lower  efficiency.  It  is  customary,  there- 
fore, when  possible,  to  supply  several  sets  of 
secondary  conductors,  say  in  several  adjacent 
buildings  from  a  single  large  transformer, 
rather  than  have  a  transformer  for  each 
house.  For  the  same  reason,  where  single 
lamps  have  to  be  supplied  by  alternating 
currents  at  considerable  distances  apart,  as,  r 
for  example,  in  street  lighting,  instead  of 

employing  a  small  ^th  KW  transformer 

for  each  lamp,  the  method  is  adopted  of 
connecting  a  number  of  lamps  in  series, 
as  in  an  arc  circuit,  and  shunting  each  lamp 
by  a  coil  called  a  reactive  coil.  This  reac- 
tive coil  allows  almost  the  entire  current 
strength  in  the  circuit  to  pass  through  the 
lamp  and  takes  only  a  small  portion 
through  its  own  circuit.  If,  however,  the 
lamp  filament  breaks,  thus  interrupting  the 


ALTERNATING-CURRENT   CIRCUIT.       399 

circuit  of  that  lamp,  the  reactive  coil  per- 
mits the  full  current  strength  to  pass 
through  it  with  only  a  comparatively  small 
drop  in  pressure;  namely,  the  pressure 


FIG.  137. — SERIES-CONNECTED  STREET  LAMP  FOR  ALTER 
NATING-CURRENT  CIRCUITS. 

equal  to  that  of  the  lamp  which  has  be- 
come extinguished.  This  drop  is  due  to  a 
C.  E.  M.  F.  established  by  the  current  in 
the  circuit  in  passing  through  the  reactive 
coil.  Such  a  series  lamp  shunted  by  its 
reactive  coil  is  represented  in  Fig.  137. 


400      ELECTRIC    INCANDESCENT   LIGHTING. 

The   alternating   currents    required   for 
alternating-current   incandescent    lighting, 


FIG.  138. — ALTERNATING-CURRENT  GENERATOR. 

are  obtained  from  a  form  of  dynamo  known 
as  an  alternator.     This  dynamo  does  not 


ALTERNATING-CURRENT   CIRCUIT.       401 

differ  in  principle  from  an  ordinary  con- 
tinuous-current generator,  except  that  it 
does  not  commute  the  current  in  its  line 
circuit.  Fig.  138,  shows  a  form  of  alter- 
nator having  fourteen  poles.  Since  the 
fourteen  field  magnet  coils  require  to  be 
supplied  by  continuous  currents,  the  ma- 
chine is  accompanied  by  a  small  continu- 
ous-current generator,  called  an  exciter. 

Incandescent  lamps,  intended  for  alter- 
nating-current circuits,  possess  no  peculiar- 
ity, that  is  to  say,  a  lamp  may  be  used 
indifferently  on  a  continuous  or  on  an  alter- 
nating-current circuit,  when  the  working 
pressures  in  each  case,  and  the  sockets,  are 
the  same. 


CHAPTEK  XX. 

MISCELLANEOUS    APPLICATIONS    OF    INCANDES- 
CENT   LAMPS. 

BESIDES  the  various  uses  for  the  incan- 
descent lamp,  which  we  have  described, 
there  are  many  others  which  want  of  space 
will  prevent  our  discussing,  except  very 
briefly. 

The  fact  that  the  incandescent  lamp  is 
capable,  within  reasonable  limits,  of  being 
made  of  almost  any  size,  and  the  additional 
fact  that  the  glowing  filament  is  entirely 
protected  by  a  surrounding  glass  chamber, 
permits  the  incandescent  lamp  to  be 
employed  for  purposes  in  which  other 
artificial  illuminants  would  be  impossible.. 


MISCELLANEOUS   APPLICATIONS.         403 

We  may  mention,  as  one  of  such  purposes, 
the  employment  of  small  suitably  shaped 
incandescent  electric  lamps  for  exploring 
the  cavities  of  the  body.  Incandescent 
lamps  are  thus  employed  by  physicians 
and  surgeons.  For  this  purpose  a  small 
lamp,  shaped  so  as  to  permit  of  its  ready 
introduction  into  the  cavity  to  be  exam- 
ined, is  mounted  at  the  extremity  of  a 
suitable  support.  In  some  cases  the  ex- 
ploring lamp  is  sometimes  placed  in  a 
sheath  or  tube,  through  the  interior  of 
which  the  illumined  area  is  directly  ob- 
served. 

An  entirely  distinct  method,  however, 
from  the  preceding  is  sometimes  adopted  ; 
namely,  the  method  of  trans-illumination. 
Here  an  attempt  is  made  to  illumine  the  in- 
terior cavity  so  as  to  permit  it  to  be  visible 
through  the  body  as  a  translucent  screen. 


404      ELECTRIC    INCANDESCENT   LIGHTING. 

The  amount  of  light  required  to  attain 
this  result,  is  so  great  as  to  necessitate  the 
liberation  of  considerable  heat  activity,  and 
means  have  usually  to  be  provided  for 
keeping  the  lamp  cool.  This  is  done  by  a 


FIG.  139. — MINIATURE  INCANDESCENT  LAMPS. 

jacket,  in  the  exterior  glass  globe,  through 
which  cold  water  is  kept  circulating. 

Examples  of  three  small  lamps  employed 
for  surgical  and  dental  purposes  are  seen 
in  Fig.  139.  Such  lamps  are  generally 
called  battery  lamps,  because  they  are  cap- 


MISCELLANEOUS    APPLICATIONS. 


405 


able  of  being  operated  from  a  primary 
or  secondary  battery.  The  usual  voltage 
is  from  three  to  six  volts.  The  efficiency 
of  such  lamps,  in  candle-power  per  watt,  is 


3-Candle  Lamp.  4-Candle  Lamp.  6-Candle  Lamp. 

FIG.   140. — MINIATURE  INCANDESCENT  LAMPS. 

much  less  than  that  of  larger  lamps,  owing 
principally  to  the  rapid  conduction  of  heat 
from  the  short  filament  through  the  con- 
ducting wires.  Other  forms  of  battery 
lamps,  of  candle-power  as  marked,  are  re- 
presented in  Fig.  140. 


406      ELECTRIC   INCANDESCENT   LIGHTING. 

Sometimes  in  medical  or  surgical  ex- 
aminations, a  small  incandescent  lamp  is 
mounted  before  a  concave  reflector,  strapped 


FIG.  141.  —INCANDESCENT  LAMPS,  WITH  REFLECTOR  AND 

CONDENSING  LENS. 

to  the  head  of  the  observer.  In  other  cases 
the  lamp  and  reflector  are  mounted  as 
shown  in  Fig.  141,  within  a  tube  mounted 


MISCELLANEOUS   APPLICATIONS.         407 

on  a  suitable  stand  and  provided  with  a 
condensing  lens. 

Another  use  for  the  incandescent  elec- 
tric lamp  which  is  due  to  the  fact  that  the 
glowing  filament  is  hermetically  sealed,  is 
the  use  of  safety  incandescent  lamps  in 
mines,  where  the  presence  of  fire-damp  is 
feared.  This  form  of  safety  lamp  is  in- 
tended to  replace  the  Davy  safety  lamp. 
Such  lamps  are  supplied  by  either  a  pri- 
mary or  secondary  battery  placed  in  the 
lamp  case.  A  form  of  such  lamp  is  shown 
in  Fig.  142. 

Battery  or  miniature  incandescent  lamps 
are  also  often  employed  for  use  with  the 
microscope  in  the  illumination  of  the 
object,  since  they  are  capable  of  being 
placed  conveniently  for  observation.  Va- 
rious designs  of  supports  and  reflectors  are 


408      ELECTRIC    INCANDESCENT   LIGHTING. 

employed   in   connection   with   lamps   for 
this  purpose. 

The  incandescent   lamp   is   used  exten- 


FIG.  142. — SAFETY  LAMP  FOR  MINES. 

sively  on  the  modern  steamship  not  only 
for  purposes  of  general  illumination  of  the 
vessel,  but  also  for  the  lighting  of  the 


409 

stern-lights 
case  of  such 
lights,  it  is  a  matter  of  considerable  im- 
portance that  the  continuity  of  service  of 
the  lamps  be  ensured,  since  the  rupture 
of  the  filament  might  jeopardize  the  vessel. 
In  order  to  lessen  the  liability  of  disabling 
the  side-light,  it  is  common  to  employ  a 
double-filament  lamp,  sometimes  called  a 
twhi-filament  lamp,  so  arranged  that  if  one 
filament  should  fail,  the  other  may  con- 
tinue burning.  At  other  times  two  sep- 
arate lamps  are  employed  for  the  same 
purpose.  A  double-filament  lamp  is  shown 
in  Fig.  143. 

Incandescent  lamps  on  board  ship  are 
operated  at  pressures  between  100  and  120 
volts,  almost  invariably  on  the  two-wire 
system.  In  warships,  the  pressure  is  usu- 
ally 80  volts,  in  order  to  facilitate  the  use 


410      ELECTRIC   INCANDESCENT   LIGHTING. 


FIG.  143. — DOUBLE  FILAMENT  LAMP  FOR  SHIP'S 
SIDE-LIGHT. 


MISCELLANEOUS   APPLICATIONS.      411 

of  arc-light  projectors  without  the  addition 
of  much  resistance  in  the  projector  circuits. 

In  the  early  history  of  ship  lighting,  the 
method  was  adopted  of  employing  the 
ship's  iron  sheathing  as  a  common  return  ; 
that  is,  one  pole  of  all  the  lamps  and  also 
one  pole  of  the  dynamo  being  connected  to 
the  sheathing  of  the  vessel,  the  other  pole 
being  connected  to  insulated  conductors. 
This  method  was,  however,  found  objec- 
tionable in  practice  and  has  been  completely 
given  up.  Especial  care  has  to  be  given 
to  the  insulation  of  wires  and  fixtures  on 
board  of  ship.  The  connection  boxes, 
switches,  etc.,  are  often  arranged  so  as  to 
be  rendered  completely  water-tight.  In 
Fig.  144,  JTj  is  the  switch  handle,  and  H, 
the  receptacle  for  the  insertion  of  local 
connecting  wires,  leading  to  the  lamp  or 
other  device  to  be  operated.  The  cover 


4:12      ELECTRIC   INCANDESCENT   LIGHTING. 

C\  is   intended  to  effect  a  water-tight  seal 
when  the  receptacle  is  removed.     In  Fig. 


FIG.  144. — WATER-TIGHT  MARINE  SWITCH  'AND  RECEP- 
TACLE. 

145,  the  switch  handle  H,  is  recessed  into 
the  water-tistfit  box  in  such  a  manner  that 

O 

the  cover  6y,  can  enclose  it  in  a  water-tight 


MISCELLANEOUS    APPLICATIONS.         413 

seal.     The  wires  enter  the  box  through  the 
water-tight  openings  at  O  O. 

Miniature  incandescent  lamps  are  occa- 
sionally employed  as  a  variety    of   electric 


FIG.  145. — WATER-TIGHT  MARINE  SWITCH. 

jewelry,  as  in  a  scarf  pin  or  ornament  for 
the  hair,  such  lamps  being  always  operated 
from  a  small  battery  carried  on  the  person. 
Similar  lamps  are  also  employed  on  the 


414      ELECTRIC   INCANDESCENT   LIGHTING. 

stage,  for  stage  effects,  being  worn  by  the 
actors. 

Incandescent  lamps  are  colored  either 
by  employing  globes  of  tinted  glass,  or  by 
dipping  the  clear  lamp  globes  into  a  solu- 
tion of  suitable  dye.  In  the  former  case 
the  coloring  is  permanent,  in  the  latter 
case,  it  is  temporary. 

Incandescent  lamps,  either  plain  or  col- 
ored, are  extensively  employed  in  illumi- 
nated electric  signs,  where  the  lamps  are 
grouped  in  the  shapes  of  letters.  Some- 
times, in  order  to  attract  attention  to  the 
sign,  automatic  switch  devices  are  em- 
ployed, which  at  intervals  extinguish  some 
or  all  of  the  lamps ;  or,  blocks  of  lamps  are 
arranged  so  as  to  be  automatically  cut  out 
of  circuit  and  cause  letters  to  successively 
appear  and  disappear  and  words  to  be  thus 
spelled  out. 


416      ELECTRIC   INCANDESCENT   LIGHTING. 

The   in  -indescent    electric   liii'ht    lends 

o 

itself  very  readily  to  decorative  effect. 
This  arises  not  only  from  the  readiness 
with  which  the  light  is  subdivided  and 
distributed,  but  also  from  the  fact  that  the 
glowing  filament  being  protected  by  the 
surrounding  glass  chamber,  permits  the 
light  to  be  partially  buried  in  walls  or 
ceilings,  in  a  manner  which  would  be  im- 
possible with  any  other  form  of  artificial 
illuminant. 

No  description  of  decorative  effect  by 
incandescent  lamps  would  be  complete 
without  some  allusion  to  the  magnificent 
spectacle  that  was  afforded  by  the  incan- 
descent lighting  of  the  Court  of  Honor,  at 
the  World's  Columbian  Exhibition,  at  Chi- 
cago, in  1893.  A  faint  conception  only  of 
the  beauty  of  this  scene  may  be  gathered 
from  the  accompanying  illustration  in  Fig. 


MISCELLANEOUS    APPLICATIONS.         417 

146.  The  building  in  the  background  is 
the  Administration  Building,  whose  exte- 
rior is  lighted  by  incandescent  lamps.  On 
the  right  hand  side  is  the  facade  of  Elec- 
tricity Building,  and  on  the  left  hand  is 
the  facade  of  Machinery  Hall.  The  entire 
bank  of  the  waterway  was  illumined  by 
incandescent  lamps. 


INDEX. 


Actinic  Effect  of  Light,  208. 
Activity,  62. 

and  Candle-Power,  Relation  Between,  183. 

,  Surface,  of  Incandescent  Filament,  165. 

,  Surface,  of  Positive  Crater  in  Arc.  166, 

,  Unit  of,  63. 

Adapters  for  Lamps,  133,  134. 
Adjustable  Lamp  Pendant,  240. 
Age  Coating  of  Lamp,  178. 
Air  Pump,  Mechanical,  125. 

Alternating-Current     Circuit    for      Incandescent 
Lighting,  386  to  401. 

Current  Generator,  400. 

Current  Transformer,  393. 

Alternation,  386. 

,  Frequency  of,  387. 

Alternator,  400. 
Ammeters,  306. 

419 


420  t     INDEX. 

Ampere,  56. 
Hours,  335. 

-  Efficiency  of  Storage  Cell,  372. 
Amyloid,  Use  of,  for  Filaments,  87, 
Analysis  of  Light  of  Glowing  Filament,  74. 

-  of  Sunlight,  74. 

Antimonious  Lead,  Use  of,  in  Storage  Cells,  354. 

Arc,  Voltaic,  18. 

Armature  for  Central-Station  Generator,  Winding 

of,  322,  323. 
—  of  Central-Station  Generator,  314. 

Artificial  Illtiminants,  Requisites  for,  C. 

Illumination,  1  to  17. 

Automatic  Cut-Out    for  Storage-Battery  Switch- 
board, 365. 

Safety  Device  for  Incandescent  Lamp,  375. 

Switch,  273. 

B 

Bamboo  Filament,  107. 

-  Filament,  Preparation  of,  86,  87. 
Bases,  Lamp,  131,  132. 

Batteries,  Storage,  345  to  373. 
Battery  Incandescent  Lamps,  407. 

-of  Boilers,  311. 
,  Voltaic,  47. 


INDEX.  421 

Begohrn,  247. 

Belt-Driven  Generator,  327. 

Belting,  327. 

.Bipolar  Generator  for  Isolated  Plant,  330. 

Blackening  of  Lamp  Chamber,  178. 

Block,  Branch,  274,  275. 

Blowing  of  Fuse,  276. 

Boilers,  Battery  of,  311. 

Bougie-Decimate,  200. 

Boulyguine,  33. 

Boulyguine's  Incandescent  Lamp,  32,  33. 

Box,  Carbonizing,  93. 

Boxes,  Distribution,  280,  282. 

,  Connecting,  263,  264. 

,  Coupling,  295,  296. 

,  Field  Regulating,  306. 

,  Junction,  300  to  303. 

Bracket,  Lamp,  243. 

—  Lamp,  Movable  Arm  for,  246. 
Branch,  274,  275. 

Coupling  Boxes,  297. 

Cut-Out,  274. 

Branches,  251. 

Brass- Covered  Conduit,  262. 

Brilliancy,  181. 

of  Incandescent  Filament,  168. 

British  Candle,  199. 


422  INDEX. 

Brushes  for  Generator,  316. 
Bus  Bars,  Definition  of,  223. 

c 

Candle   Power   and  Activity,  Relation  Between, 

183. 
• Power,  Effect  of  Varying  Pressure  on,  188 

to  191. 

Power  of  Luminous  Source,  199. 

Power,  Mean  Spherical,  207. 

Capacity,  Energy  of,  Storage  of  Cell,  361. 

,  Storage,  349. 

Carbon  Filament,  Life  of,  16V. 

,  Suitability  of,  for  Incandescent  Filament, 

83,  84. 
Carbonization,  General  Processes  for,  84,  85. 

,  Methods  Employed  for,  91  to  98. 

Carbonizing  Box,  93. 

Frame,  94,  95. 

Cell,  Charged,  352. 

,  Counter-Electromotive  Force  of,  365. 

,  Secondary,  352. 

Celluloid  Filaments,  90. 

Central-Station   Generator,  Double   Brushes    for, 

316. 
Station  Generators,  313. 


INDEX.  423 

Central  Station,  Load  Diagram  of,  347,  348. 

Station,  Six-Pole  Generator  for,  317  to  320. 

Station  Smashing  Point  of  Lamp,  193. 

Station,  Storage  Cell  for,  359. 

Station  Switchboard,  305  to  308. 

Central  Stations,  304  to  333. 

Charged  Cell,  352. 

Charging  Current,  352. 

Chlorine  and  Bromine,  Residual  Atmospheres  of, 

in  Lamp  Chambers,  130. 
Circuit,  Open,  46. 

,  Primary,  of  Transformer,  393. 

,  Secondary,  of  Transformer,  394. 

,  Series  Arc  and  Incandescent,  383. 

Circular-Mil,  Definition  of,  54. 
Circular-Mil-Foot,  54. 
Cleat  Wiring,  254. 
Cleats,  255. 

,  Wooden,  255. 

Coil,  Reactive,  398. 
Cold  Light,  10,  78,  79. 
Color,  Cause  of,  71,  72. 

Values,  Day-Light,  72. 

Commutator  of  Central-Station  Generator,  314. 

,  Sparking  at,  317. 

Concave  Panel  Shade  and  Reflector,  153. 
Concealed  Work,  260. 


424  INDEX. 

Conduction  of  Heat,  75. 

Conductor,  Neutral,  of  Three-Wire  System,  222. 

— ,  Twisted-Double,  248. 
Conductors,  Double-Flexible,  249. 
,  Drop  in,  252. 

— ,  Parallel,  248. 

— ,  Silk-Covered,  248. 

— ,  Solid,  247. 

— ,  Supply,  250. 

— ,  Twin,  248. 

,  Stranded,  247. 

Conduit,  Brass-Covered,  262. 

of  Creosoted  Wood,  288,  289. 

Conduits,  287. 

,  Interior,  261,  262. 

Connecting  Boxes,  263,  264. 

Connection  Boxes  for  Interior  Conduits,  264. 

in  Series,  47. 

Consumers'  Smashing  Point  of  Lamp,  194. 
Continuous  Electric  Current,  304. 
Convection  of  Heat,  77. 
Cord,  Flexible  Lamp,  240. 
Corrugated  Lamp  Reflector  and  Shade,  155. 
Cotton  Thread,  Use  of,  for  Filament,  87. 
Coulomb,  56. 
Coulomb-per-Second,  56. 
Counter-Electromotive  Force  Cells,  365. 


INDEX.  425 

Coupling  Boxes,  295. 

—  Boxes,  Branch,  297. 
Crater,   Positive,   of    Arc,   Surface    Activity   in, 

166. 

Creosoted  Wood  Conduit,  288,  289. 
Current,  Continuous  Electric,  304. 

,  Electric,  Pulsating,  386. 

,  Steady  Electric,  386. 

Strength,  Effective,  391. 

Cut-Out,  Branch,  274. 

Film  for  Incandescent  Electric  Lamp,  376, 

377. 

-  Fixture,  278,  279. 

-  Mains,  277. 

Switch  for  Series  Circuit,  384. 

Cycle,  387. 

D 

Day-Light  Color  Values,  72. 
De  Changy,  25. 

Incandescent  Lamp,  26,  27. 

De  Moleyn,  24. 

Diagram  of  Central-Station  Load,  347,  348. 

Direct-Driven  Generator,  328,  329. 

Distributing  Point,  280. 

Distribution  Boxes,  280,  283. 


426  INDEX. 

Distribution,  Centers  of,  253. 

,  Series-Multiple  Lamp,  221. 

,   Three- Wire   System    of   Lamps,    221    to 

224. 
Double    Brushes    for  Central-Station    Generator, 

316. 

Filament  Lamps,  409. 

Flexible  Conductors,  249. 

-  Pole  Switches,  267. 

—  Pole  Switches,  Forms  of,  269,  270,  271. 
Drop  in  Conductors,  252. 
Dummy  Moulding,  260. 
Dynamo-Electric  Generator,  48. 
Dynamos  or  Generators,  311. 


E 

E.  M.  F.,  44. 

Early  History  of  Incandescent  Lighting,  18 
to  42. 

Early  Horse-Shoe  Lamp,  104. 

Early  Illuminants,  1  to  5. 

Incandescent  Lamps,  19,  20. 

Effect  of  Temperature  on  Resistivity  of  Insula- 
tors, 55. 

Effective  Current  Strength,  391. 

Efficiency,  Ampere-Hour,  of  Storage  Cell,  372. 


INDEX.  427 

Efficiency  of  Incandescent  Lamp,  170  to  233. 
'  of  Lamp,  Effect  of,  on  Duration  of  Life, 

184,  185. 

of  Storage  Cell,  372. 

of  Transformers.  395. 

Electric  Jewellery,  413. 

Lighting,  Life  Risks  of,  14,  15. 

Pressure,  45. 

Quantity,  Unit  of,  56. 

Resistance,  49. 

Electrolier,  243. 

Electrolytic  Meter,  335  to  339. 

Seal,  108. 

Electromotive  Force,  43. 
Elementary  Electrical  Principles,  43  to  64. 
Elements  or  Plates  of  Storage  Cell,  351. 
Emissivity  of  Incandescing  Filament,  80,  81. 
of  Lamp  Filament,  Effect  of  Surface  on, 

180. 
Energy  Efficiency  of  Storage  Cell,  372,  373. 

Storage  Capacity  of  Secondary  Cell,  361. 

Storage  of  Cell,  361. 

Equalizer  Switch,  235,  236. 
Ether,  Luminiferous,  67. 

,  Universal,  67. 

Evaporation  of  Incandescent  Filament,  176,  177. 
Exciter,  401. 


428  INDEX. 

F 

Factor,  Load,  349. 

Farmer,  36. 

Farmer's  Incandescent  Lamp,  35,  36. 

Feeder  Distribution,  229. 

Distribution,  Three- Wire  System  of,  231, 

232. 
Equalizer  Resistance,  234. 

—  Load,  Methods  of    Overcoming    Inequali- 

ties of,  233,  236. 

—  Regulators,  233. 
-  System,  253. 

—  Tubes,  298,  299. 

Feeders  for  Lamp  Distribution,  228. 

Feeding  Point,  298. 

Field  Magnet  Coils  of  Generator,  314. 

Regulating  Boxes,  306. 

Filament,  Bamboo,  Preparation  of,  86,  87. 

— ,  Effect  of  Flashing  on  Emissivity  of,  116, 
117. 

— ,  Effect  of  Surface  on  Emissivity  of,  180. 

— ,  Incandescing,  Surface  Activity  of,  80,  81. 

— ,  Mounting  of,  99,  100, 
,  Sealing-in  of,  118. 

— ,  Shadows,  1/9. 

— ,  Spotted,  112. 


Filaments,  Amyloids, 

— ,  Celluloid,  90. 

,  Flashing  Process 

,  Methods  Employed  for 

91  to  98. 

— ,  Squirted,  88,  89,  97. 

— ,  Stopper-Mounted,  122,  123. 

— ,  Use  of  Cotton  Thread  for,  87. 
Fire  Fly,  Radiation  of,  78. 
Fittings,  Lamp,  135  to  162. 

Five-  and  Four-Wire  Systems  of  Lamp  Distribu- 
tion, 225. 
Fixture  Cut-Outs,  278,  279. 

—  Molding,  259. 

for  Street  Incandescent  Lamp,  381,  382. 

Fixtures  and  Wiring  for  Houses,  237  to  283. 
Flashing  Process  for  Filaments,  113,  114,  115. 
Flexible  Lamp  Cord,  240. 

—  Lamp  Pendant,  239,  240. 
Flush  Switches,  272. 
Foot-Pound,  59. 
Foot-Pound-per-Second,  63. 

Four-  and  Five-Wire  Systems  of  Lamp  Distribu- 
tion, 225, 

Frame,  Carbonizing,  94,  95. 
French  Standard  Candle,  200. 
Frequency,  Effect  of,  on  Steadiness  of  Light,  388. 


430  INDEX. 

Frequency  of  Alternation,  387. 

,  Luminous,  68. 

Full- Wire  Guard  for  Incandescent  Lamp,  158. 
Fuse,  Blowing  of,  276. 

— ,  Cut-Out,  273. 

— ,  Safety,  274. 

G 

Geissler  Type  of  Mercury  Pump,  127. 
Generator,  Alternating-Current,  400 

,  Dynamo-Electric,  48. 

,  Field  Magnet  Coils  of,  314. 

Unit,  308. 

Generators,  Multipolar,  316. 

Generators  or  Dynamos,  313. 

Glass  Lamp  Shades,  156. 

Glow  Worm  and  Fire  Fly,  Radiation  of,  78. 

Glowing  Filament,  Analysis   of   Light  Produced 

by,  74. 
Grids  of  Storage  Cell,  351. 

H 

Half-Shade  for  Incandescent  Lamp,  151. 
Half  Wire-Guard  for  Incandescent  Lamp,  157. 
Heat,  Conduction  of,  75. 
,  Convection  of,  77. 


INDEX.  431 


Heat,  Molecular  Transfer  of,  76,  77. 

•,  Radiation  of,  75. 

High-Economy  Lamps,  389. 
Horizontal  Intensity,  Maximum,  207. 
Horse-Power,  Definition  of,  63. 
Hours,  Ampere,  335. 

,  Watt,  335. 

House  Fixtures  and  Wiring,  237  to  283. 


Illuminants,  Early,  1  to  5. 
Illuminated  Electric  Signs,  414. 
Illumination,  Actual  Values  of,  206. 

,  Artificial,  1  to  17. 

,  Law  of,  203,  204,  205. 

,  Significance  of,  198. 

,  Unit  of,  202. 

Incandescent  Lamp,  163. 

Lamp,  Automatic  Safety  Device  for,  375. 

Lamp,  Efficiency  of,  170  to  233. 

-  Lamp,  Half  Wire-Guard  for,  157. 
Lamp,    Multiple-Series     Distribution    of, 

376,  377. 
Lamp,  Street  Fixture  for,  378. 

-  Electric  Lamp,  Film  Cut-Out  for,  376,  377. 
Electric  Lamp,  Physics  of,  65  to  82. 


432  INDEX. 

Incandescent  Filament,  Brilliancy  of,  168. 
Filaments,  Evaporation  of,  176,  177. 

-  Filament,  Total  Candle-Power  of,  168, 169. 

-  Filaments,  Surface  Activity  of,  165. 
Lamp,  Full  Wire-Guard  for,  158. 

-  Head-Lights  for  Ships,  409. 
Lamps,  Early,  19,  20. 

-  Lamps,  Miniature,  404,  405. 

Lamps,     Miscellaneous    Applications    of, 

402  to  417. 

Lamp,  Varying  Candle-Powers  of,  209. 

Lighting,  Early  History  of,  18  to  42. 

—  Lighting,  Fire  Risks  of,  13,  14. 
— —  Lighting,  Alternating-Current  Circuit  for 

386  to  401. 

Lighting,  Decorative  Effects  in,  416,  417. 

• •  Side-Lights  for  Ships,  409. 

Signal  Lights  for  Ships,  409. 

Stern-Lights  for  Ships,  409. 

Filament,  Emissivity  of,-80,  81. 

Filament,  Temperature  of,  82,  174. 

Intake  Wires,  280. 
Intensity,  Luminous,  69. 

,  Maximum  Horizontal,  207. 

Interior  Conduit  Joints,  263. 

Conduit  Junction  Boxes,  264. 

Conduit,  Junction  Boxes  for,  265. 


INDEX.  433 

Interior  Conduits,  261,  262. 
Isolated  Lighting  Plants,  324  to  333. 

—  Plant,  Smashing  Point  of  Lamps,  194,  195. 

-  Plants,  324  to  333. 
Plants,  Quadripolar  Generator  for,  330,  332. 


Jewellery,  Electric,  413. 

Joints  of  Filament  with  Leading-in- Wires,  Bolt 

and   Nut  Type,  108. 
,  Butt  Joint  Type,  111. 

— ,  Socket  Type,  108. 

— ,  Interior  Conduit,  263. 
Joule,  60. 

Joule-per-Second,  63. 
Junction  Boxes,  300  to  303. 
Interior  Conduit,  264. 

K 

Keyless  Wall-Socket,  138. 
Key-Socket  Push  Button,  145. 

—  Wall-Socket,  139. 
Keys  for  Sockets,  140  to  142.     . 
King,  27. 
Kosloff,  29. 
Konn,  29. 
Komi's  Incandescent  Lamp,  30,  31. 


434  INDEX. 


Lamp  Adapter,  133. 

,  Age-Coating  of,  178. 

-  Bases,  131,  132. 

-  Bracket,  243. 

Chamber,  Blackening  of,  178. 

,  Filament  Shadows  on,  179. 

— ,  Machine  Sealing  of,  121. 
— ,  Sealing  Off  of,  127,  128. 

,  Steam-Tight,  161,  162. 

Cord,  Flexible,  240. 


—  Cords,  Silk,  248. 

—  Distribution,  Series-Multiple  System  of,  221. 
— ,  Distribution  Systems  of,  209  to  236. 

—  Filament,    Relation    Between    Efficiency, 

Candle-Power,  and  Surface  Activity  of, 
180. 

—  Fittings,  135  to  162. 

—  Guard,  Portable,  160. 
— ,  Incandescent,  163. 

— ,  Leading-in- Wires  of,  100. 

— ,  Mean  Spherical  Candle-Power  of,  207. 

—  Pendant,  Adjustable,   240. 
— ,  Flexible,  239,  240. 

— ,  Portable  Incandescent,  238. 

—  Post  for  Incandescent  Lamps,  380,  381. 


INDEX.  435 

Lamp  Reflector  and  Shade,  Corrugated,  155. 

Renewals,    Rules    for    Best    Commercial 

Results,  196,  197,  198. 

Shades,  Glass,  156. 

Shadows,  149  to  156. 

,  Smashing  Point  of,  192. 

,  Semi-Incandescent,  37,  38,  39, 

Socket,  Temporary,  147. 

Socket,  Weather-Proof,  148. 

Sockets,  135  to  140. 

,  Stopper,  121,  122,  123. 

Switch,  140. 

Switches,  267. 

,  Twin-Filament,  409. 

Lamps,  Battery-Incandescent,  407. 

— ,  Connection  in  Parallel,  210. 

,  Diagram  of  Multiple  Connection  of,  212. 

,  Distribution  of  by  Four-  and  Five-Wire 

Systems,  225. 

,  Double-Filament,  409. 

,  Incandescent,  Use  of,  for  Surgical  Explo- 
ration, 403. 

,  Miniature  Incandescent,  404. 

,  Safety  Incandescent,  407. 

,  Series  Connected,  Diagram  of,  211. 

— ,  Series  Connections  of,  210. 

,  Spring  Socket  for,  146. 


436  INDEX. 

Lamps,  Tree  Distribution  of,  230. 

Law  of  Illumination,  203. 

Leading-in  Wires  of  Lamp,  100. 

Life  of  Filament,  Circumstances  Governing,  167. 

of  Incandescent  Filament,  167. 

-  of  Lamp  and  Efficiency,  Relation  Between, 

183. 

Light,  Actinic  Effect  of,  208. 
,  Monochromatic,  73. 

— ,  Objective,  Significance  of,  66. 

,  Significance  of  term,  198. 

,  Subjective,  Significance  of  term,  66. 

— ,  Two-Fold  Use  of  Word,  66. 

— ,  Unit  of  Total  Quantity  of,  201. 
Lighting  Plant,  Isolated,  325. 

,  Series  Incandescent,  374  to  385. 

Load  Diagram  of  Central  Station,  347,  348. 

—  Factor,  348. 
Lodyguine,  28. 

Long  Life  vs.  Low  Efficiency,  185,  186. 
Lumen,  201. 
Luminiferous  Ether,  67. 
Luminous  Frequency,  68. 

Frequency,    Effect    of    Temperature    on, 

68,  69. 

Intensity,  69. 

Intensity,  Standards  of,  200. 


INDEX.  437 


Luminous  Intensity,  Unit  of,  199. 

—  Source,  Candle-Power  of,  199. 
Lux,  202. 
Lux-Second,  208. 

M 

Machine  Seal  of  Lamp  Chamber,  121. 
Main  Conductors,  Overhead,  284. 

-  Cut-Outs,  277. 

-  Switch,  277. 
Tubes,  293. 


Mains,  250. 

— ,  Street,  284  to  303. 

— ,  Three- Wire,  276. 

— ,  Two- Wire,  276. 
Man  Holes,  287. 
Marine  Switch  for  Lamps,  412. 
Maximum  Horizontal  Intensity,  207. 
Mean  Spherical  Candle-Power,  207. 
Mechanical  Air  Pump,  125. 
Mercury  Pump,  125. 

—  Pump,  Geissler  Type,  127. 
Mercury  Pump,  Sprengel  Type,  127. 
Metallic  Half-Shade  for  Incandescent  Lamp,  151, 

• Lamp  Shades,  149  to  153. 

Meter,  Electrolytic,  335  to  339. 
Meters,  Electric,  334,  344. 


438  INDEX. 

Methods   for   Overcoming    Inequality   of   Feeder 
Loads,  233,  236. 

Mil-Foot,  Circular,  Definition  of,  54. 

Miscellaneous  Applications  of  Incandescent  Lamps, 
402  to  417. 

Molecular  Transfer  of  Heat,  76,  77. 

Monochromatic  Light,  73. 

Molding,  Dummy,  260. 

,  Picture  or  Ornamental,  259. 

— ,  Section  of,  258. 

,  Three- Wire,  257. 

Mounting  of  Filament,  99,  100. 

Movable  Arm  for  Bracket  Lamp,  246. 

Multiple  and  Series  Systems  of  Lamp  Distribution, 
Relative  Advantages  of,  212  to  220. 

Connected  Lamps,  Diagram  of,  212. 

Series  System   of   Distribution  of   Incan- 
descent Lamps,  376,  377. 

Multipolar  Generators,  316. 

N 

Negative  Plate  of  Storage  Cell,  351. 

Pole,  44. 

Terminal,  44. 

Neutral  Conductor  of  Three- Wire  System,  222. 
Non-Luminous  Heat,  10. 


INDEX.  439 

o 

Occluded  Gas  Process,  128,  129. 
Ohin,  57. 

,  Definition  of,  50. 

Ohm's  Law,  57. 

Open-Circuit,  46. 

Ornamental  Moulding,  259. 

Outlet  Boxes,  266. 

Output  Wires,  282. 

Overhead  Main  Conductors,  284. 

Wires,  284. 

Overload    Switch    for   Storage    Battery    Switch- 
board, 366  to  370. 


Panel  Reflectors,  153,  154. 

Parallel  Conductors,  248. 

Parchmentizing  Process,  85,  86. 

Pendant  Lamp,  244. 

Petrie,  24. 

Phot,  208. 

Physics  of  the  Incandescent  Lamp,  65  to  82. 

Plant  for  Isolated  Lighting,  325. 

Plants,  Isolated,  324  to  333. 

Plates  or  Elements  of  Storage  Cell,  351. 


440  INDEX. 

Platinum- Wire   Incandescent   Lamps,    Requisites 
for,  21,  22. 

—  Wire,  Use  of,  for  Sealing-in  Lamp  Chamber, 

105. 

Plug,  Cut-Outs,  277. 
Point,  Distributing,  280. 

,  Feeding,  298. 

Pole,  Negative,  44. 

,  Positive,  44. 

Portable  Electric  Incandescent  Lamp,  238. 

—  Lamp  Guard,  160. 
Positive  Plate  of  Storage  Cell,  351. 

-  Pole,  44. 

—  Terminal,  44. 
Pressure,  Electric,  45. 

— ,  Unit  of,  46. 

—  Switch  for  Storage  Battery  Switchboard, 

364. 

Wires,  298. 

Primary  Circuit  of  Transformer,  393. 
Pulsating  Electric  Current,  386. 
Pump,  Mercury,  125. 
Push-Button  Key  Socket,  145. 

Q 

Quadripolar  Generator  for  Isolated  Plants,  330,  332. 


INDEX.  441 

R 

Radiation  of  Glow- Worm  and  Fire-Fly,  78. 

-  of  Heat,  75. 
Rate-of- Doing-  Work,  62. 
Radiation,  Selective,  79. 
Rays,  Ultra-Violet,  70. 
Reactive  Coil,  398. 

Recording  Wattmeter,  341  to  349. 
Reflector  Shade  for  Incandescent  Lamp,  152. 
Regulators,  Feeder,  233. 
Requisites  for  Artificial  Illuminants,  6. 
Residual    Atmosphere,    Lamp    Chambers    Inten- 
tionally Provided  with,  130. 
Resistance,  Electric,  49. 

-  Electric,  Unit  of,  50. 

—  for  Feeder  Equalizer,  234. 

,  Specific,  53. 

Resistivity,  53. 

of  Conductors,  Effect  of  Temperature  on, 

55. 
of  Insulators,  Effect  of  Temperature  on, 

55. 

Reynier,  38. 

Reynier's  Semi-Incandescent  Lamp,  38,  39. 
Reynier- Werdermann's  Incandescent  Lamp,  41,  42. 
Risers,  250. 


442  INDEX. 

s 

Safety  Incandescent  Lamps,  407. 
-  Fuse,  274. 

Sawyer,  33. 

Sawyer's  Incandescent  Lamp,  34. 

Safety  Device,  Automatic,  for  Incandescent  Lamp, 
375. 

Screw  Cleats,  256. 

Seal,  Machine,  of  Lamp  Chamber,  121. 

Sealiug-in  of  Filament,  118. 

Sealing-off  of  Lamp  Chamber,  127,  128. 

Secondary  Cell,  352. 

Circuit  of  Transformer,  394. 

Selective  Absorption  of  Light  Radiations,  71,  72. 

Radiation,  79. 

Semi-Incandescent  Lamp,  37,  38,  39. 

Series  and  Multiple  Distribution,  Relative  Advan- 
tages of,  212  to  220. 

Arc  and  Incandescent  Lamp  Circuit,  383. 

Connected  Lamps,  Diagram  of,  210. 

Connection,  47. 

Connections  of  Lamps,  210. 

Incandescent  Lighting,  374  to  385. 

Multiple  System    of    Lamp    Distribution, 

221. 

Service  Wires,  250. 


INDEX.  443 

Shades  for  Incandescent  Lamps,  149  to  156. 

Shadows,  Filament,  179. 

Ship  Lighting  by  Incandescent  Lamps,  412. 

Ships,  Incandescent  Head-Lights  for,  409. 

,  Incandescent  Side-Lights  for,  409. 

,  Incandescent  Stern-Lights  for,  409. 

Short-Circuit,  272. 

Short  Life  vs.  High  Efficiency,  185,  186. 

Signal  Lights  for  Ships,  Incandescent,  409. 

Signs,  Illuminated  Electric,  414. 

Silk-Covered  Conductors,  248. 

Lamp  Cords,  248. 

Single-Pole  Switch,  Simple  Form  of,  268. 

Pole  Switches,  267. 

Six-Pole  Generator  for  Central  Station,  217  to 
320. 

Smashing  Point  of  Lamp,  192. 

Point  of  Lamp  from  Central  Station  Stand- 
point, 193. 

Point  of  Lamp  from  Consumers'  Stand- 
point, 194. 

Point  of  Lamp  from  Isolated-Plant  Stand- 
point, 194,  195. 

Socket  Keys,  140  to  142. 

Sockets,  Simple  Form  of,  137. 

Solid  Conductors,  247. 

Wires,  246. 


444  INDEX. 

Sparking  at  Commutator,  317. 

Specific  Resistance,  53. 

Spotted  Filament,  112. 

Sprengel  Type  of  Mercury  Pump,  127. 

Spring  Socket  for  Lamps,  146. 

Squirted  Filaments,  88,  89,  97. 

Starr,  27. 

King  Incandescent  Lamp,  27,  28. 

Standard  Candle,  French,  200. 

of  Luminous  Intensity,  200. 

Storage  Cell  Tester,  Simple  Form  of,  371,  372. 

Stations,  Central,  304. 

Steadiness  of  Light,  Effect  of  Frequency  on,  388, 

Steady  Electric  Current,  386. 

Steam-Tight  Lamp  Chamber,  161,  162. 

Step-Down  Transformer,  395. 

Step-Up  Transformer,  395. 

Stern-Lights  for  Ships,  Incandescent,  409. 

Stopper  Lamp,  121,  122,  123. 

Stopper-Mounted  Filaments,  122,  123. 

Storage-Battery  Switchboard,  363  to  369. 

Batteries,  345  to  373. 

Capacity,  349. 

Cell,  Efficiency  of,  2,  372. 

-  Cell,  Energy  Storage  Capacity  of,  361. 

Cell,  for  Central-Station  Work,  359. 

Cell,  Energy  Efficiency  of,  372,  373. 


INDEX.  445 

Storage  Cell,  Plates  or  Elements  of,  351. 

—  Cell,  Negative  Plate  of,  351. 
Cell,  Positive  Plate  of,  351. 

Cell,  Voltmeter  and  Electrodes,  370. 

Stranded  Wires,  246. 

Conductors,  247. 

Street  Incandescent  Lamp  Fixture,  381,  382. 

Fixture,  for  Series-Incandescent  Lamp,  378. 

Lamps,  Series  Connected  for  Use  on  Alter- 
nating-Current Circuits,  399. 

Mains,  284  to  303. 

Sub  Mains,  250. 

Subways,  285,  286. 

Sunlight,  Analysis  of,  74. 

Color  Values  of  Artificial  Illuminants,  8,  9, 

12. 

,  Frequencies  Present  in,  70. 

Supply  Conductors,  250. 

Surface  Activity  of  Incandescing  Filament,  80,  81, 
165. 

Activity  of  Lamp  Filament,  180. 

Activity  of  Positive  Crater  of  Arc,  166. 

Surgery,  Use  of  Incandescent  Lamps  in,  403. 

Suspended  Lamps,  Wire  Guards  for,  159. 

Switch,  Automatic,  273. 
— ,  Flush,  272. 

—  for  Lamps,  140. 


446  INDEX. 

Switch,  Main,  277. 

,  Marine,  for  Lamps,  412. 

,  Pressure,  for  Storage-Battery  Switch- 
board, 364. 

,  Overload,  for  Storage-Battery  Switch- 
board, 365,  366  to  370. 

Switchboard  for  Central  Station,  305  to  308. 

Switches,  Double-Pole,  267. 

for  Lamps,  267. 

,  Single-Pole,  267. 

System,  Feeder,  253. 

,  Three-Wire,  of  Lamp  Distribution,  221  to 

224. 

Systems  of  Lamp  Distribution,  210. 

T 

Taps,  251. 

Temperature,  Effect  of,  on  Luminous  Frequencies, 

68,  69. 

,  Effect  of,  on  Resistivity  of  Insulators,  55. 

of  Incandescing  Filament,  82,  174. 

Temporary  Lamp  Socket,  147. 
Terminal,  Negative,  44. 

,  Positive,  44. 

Tester  for  Storage  Cells,  Simple   Form  of,  371, 

372. 


INDEX.  447 

Thermostat,  339. 

Three-Wire  Mains,  276. 

Moulding,  257. 

System,  Neutral  Conductor  of,  222. 

System  of  Feeder  Distribution,  231,  232. 

System  of  Distribution,  221  to  224. 

Time  Illumination,  Unit  of,  208. 

Total  Candle-Power  of  Incandescent  Filament, 
168,  169. 

Transformer,  Alternating- Current,  393. 

•,  Primary  Circuit  of,  393. 

,  Step-Up,  395. 

,  Secondary  Circuit  of,  394. 

Transformers,  Effect  of  Size  and  Weight  on  Cost 
and  Efficiency  of,  397,  398. 

Efficiency  of,  395. 

Step-Down,  395. 

Trans-Illumination,  403. 

Tree  Distribution  of  Lamps,  230. 

Twin  Conductors,  248. 

Filament  Lamp,  409. 

Twisted  Double  Conductor,  248. 

Two-  and  Three-Wire  Systems  of  Lamp  Distribu- 
tion, Relative  Economy  of,  223,  224. 

Two-Wire  Mains,  276. 

Tube,  Underground,  292. 

Tubes,  Feeder,  298,  299. 


448  INDEX. 

u 

Ultra-Violet  Rays,  70. 
Underground  Tube,  292. 
Unit  Generator,  308. 

of  Activity,  63. 

• of  Electric  Activity,  63. 

-  of  Electric  Flow,  56. 

• of  Electric  Power,  63. 

of  Electric  Pressure,  46. 

—  of  Electric  Quantity,  56. 

—  of  Electric  Resistance,  50. 
of  Illumination,  202. 

of  Illumination,  Intensity  of,  199. 

of  Time  Illumination,  208. 

—  of  Total  Quantity  of  Light,  201. 

—  of  Work,  59. 
Universal  Ether,  67. 

V 

Violle,  200. 
Volt,  46. 

Ampere,  63. 

Coulomb,  61. 

Coulomb-per-Second,  63. 

Voltaic  Arc,  18. 
Battery,  47. 


INDEX.  449 

Voltmeters,  306. 

and  Electrodes  for  Storage  Cell,  370. 

w 

Wall  Socket,  Key,  139. 

Socket,  Keyless,  138. 

Watt-Hours,  335. 

Wattmeter,  Recording,  341  to  349. 

Weather-Proof  Lamp  Socket,  148. 

Werdermann,  40. 

Werdermann's  Semi-Incandescent  Lamp,  41. 

Wire-Guards  for  Suspended  Lamps,  159. 

Wires,  In -Take,  280. 

,  Overhead,  284. 

,  Pressure,  298. 

,  Service,  250. 

— ,  Solid,  246. 

— ,  Stranded,  246. 
Wiring  and  Fixtures  for  Houses,  237  to  283. 

Cleat,  254. 

Wooden  Cleats,  255. 
Work,  59. 

— ,  Concealed,  260. 
,  Unit  of,  59. 


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The  Telegraph  in  America.  By  Jas.  D.  Reid. 
894  royal  octavo  pages,  handsomely  illustrated.  Russia,  7.00 

Dictionary  of  Electrical  Words,  Terms 
and  Phrases.  By  Edwin  J.  Houston,  Ph.D. 
Third  edition.  Greatly  enlarged.  667  double  column 
octavo  pages,  582  illustrations 5.00 

The  Electric  Motor  and  Its  Applications. 

By  T.  C.  Martin  and  Jos.  Wetzler.  With  an  appendix 
on  the  Development  of  the  Electric  Motor  since  1888,  by 
Dr,  Louis  Bell.  315  pages,  353  illustrations 3.00 

The  Electric  Railway  in  Theory  and 
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Bell.  Second  edition,  revised  and  enlarged.  416  pages, 
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Alternating  Currents.  An  Analytical  and  GrapK- 
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Gerard's  Electricity.  With  chapters  by  Dr.  Louis 
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The  Theory  and  Calculation  of  Alternat- 
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Steinmetz 2.50 

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Forms.  By  H.  A.  Foster 2.50 

Continuous  Current  Dynamos  and  Motors. 

An  Elementary  Treatise  for  Students.      By  Frank  P. 
Cox,  B.  S.     271  pages,  83  illustrations 2.00 

Electricity  at  the  Paris  Exposition  of 
1889.  By  Carl  Hering.  250  pages,  62  illustrations.  2.00 

Electric  Lighting  Specifications  for  the  use  of 

Engineers  and  Architects.     Second  edition,  entirely  re- 
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The  Quadruplex.  By  Wm.  Maver,  Jr.,  and  Minor 
M.  Davis.  With  Chapters  on  Dynamo -Electric  Machines 
in  Relation  to  the  Quadruplex,  Telegraph  Repeaters,  the 
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The  Elements  of  Static  Electricity,  with  Full 
Descriptions  of  the  Holtz  and  Topler  Machines.  By 
Philip  Atkinson,  Ph.D.  Second  edition.  228  pages, 
64  illustrations 1.50 

Lightning  Flashes.  A  Volume  of  Short,  Bright 
and  Crisp  Electrical  Stories  and  Sketches.  160  pages, 
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Electricity  and  Magnetism.  Being  a  Series  of 
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Electrical  Measurements  and  Other  Ad- 
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The  Electrical  Transmission  of  Intelli- 
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Electricity  One  Hundred  Years  Ago  and 
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Alternating   Electric   Currents.      By  E.  J. 

Houston,  Ph.D.  and  A.  E.  Kennelly,  D.Sc.  (Electro- 
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Electric  Heating.  By  E.  J.  Houston,  Ph.D.  and 
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Electro-Therapeutics.  By  E.  J.  Houston,  Ph.D. 
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Electric  Arc  Lighting.  By  E.  J.  Houston,  Ph.D. 
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Electric  Incandescent  Lighting.     By  E.  J. 

Houston,  Ph.D.  and  A.  E.  Kennelly,  D.Sc.  (Electro- 
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Alternating  Currents  of  Electricity.  Their 
Generation,  Measurement,  Distribution  and  Application. 
Authorized  American  Edition.  By  Gisbert  Kapp.  164 
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Recent    Progress    in   Electric    Railways. 

Being  a  Summary  of  Current  Advance  in  Electric  Rail- 
way Construction,  Operation,  Systems,  Machinery, 
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Original  Papers  on  Dynamo  Machinery 
and  Allied  Subjects,  Authorized  American 
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Davis'  Standard  Tables  for  Electric  Wire- 
men.  With  Instructions  for  Wiremen  and  Linemen, 
Rules  for  Safe  Wiring  and  Useful  Formulae  and  Data. 
Fourth  edition.  Revised  by  W.  D.  Weaver i  .00 

Universal  Wiring  Computer,  for  Determining 
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Experiments  With  Alternating  Currents 
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Lectures  on  the  Electro-Magnet.  Authorized 
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Dynamo  and  Motor  Building  for  Amateurs. 

With  Working  Drawings.     By  Lieutenant  C.  D.  Park- 
hurst i.oo 

Reference  Book  of  Tables  and  Formulae 
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By  E.  A.  Merrill i.oo 

Practical    Information   for    Telephonists. 

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Wheeler's  Chart  of  Wire  Gauges i.oo 

A  Practical  Treatise  on  Lightning  Con- 
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Proceedings  of  the  National  Conference  of 
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Wired  Love  ;  A  Romance  of  Dots  and  Dashes.  256 
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Tables  of  Equivalents  of  Units  of  Measure- 
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